Abstract: In order to solve the problem that seedlings cultivated by pie-shaped compression matrix can not be planted by the existing transplanter, a semi-automatic compression matrix seedling transplanter was designed in this paper by mimicking the artificially transplanting method of putting seedlings after punching a hole. The compression matrix type seedling transplanter mainly consists of a ground wheel, a swing mechanism, a ratchet wheel, a hole puncher, a displacement mechanism, a seedling clamping mechanism, a conveying device, a transmission system, a rack, and so on. The physical dimensions and mechanical properties of the compression matrix type seedling are the key basis for the design of the seedling planting schemes and structures. Taking watermelon seedlings as the research object, the dimensions of the seedlings were measured, and the friction coefficient of the compression matrix with different water contents and the compressive strength of the compression matrix were determined. The coefficients of friction between the slideways and the flanks of watermelon seedlings with 2 groups of different water contents were determined to be 0.755 and 0.634 respectively by single-factor tests. The relationship between the compression load and the compression amount of the 2 groups was also analyzed. When the load is 0-5 N, as the surface of the seedling is in point contact with the semi-circular thin metal at the initial stage of compression, the compression load increases evenly and the amount increases rapidly. When the load is between 5 and 20 N, as the surface of the seedling is in surface contact with the semi-circular thin metal, the compression load increases evenly with less impact on compression. When the load is greater than 25 N, some external cracks are observed on the surface of the seeding during the test. Comparing the 2 tests, it can be seen that the seedling with high water content is not easily destroyed. The swing mechanism is optimized according to the known movement law of the initial angle of the crank and the output angle of the driven rod. The dimensions of optimized parts are 57, 161, 79 and 170 mm, respectively. When the crank rotates one revolution of 360°, the reciprocating swing angle of the driven rod is 92.3°, which satisfies the working requirements of the four-equal-part ratchet wheel mechanism. The structure and specific size parameters of the hole puncher are determined according to the measurement size and planting depth requirements of the watermelon seedling. The width of the edge surface is 1.5 mm. The inner diameter of the small end is 64 mm, and the height of the tapered part of the hole puncher is 65 mm, and when the incision angle is 21°, the inner diameter of the big end is about 114 mm. The structure parameters of the seedling clamping mechanism are determined according to the mechanical properties and the dimension of watermelon seedling. And it is also concluded that the seedling's matrix can overcome the self-gravity of the seedling, which ensures that the seedling clamping mechanism can securely grip the seedlings when transplanting with a clamping force of 26 N. The seedling conveying device and the planting holding device are driven by the same power source, ensuring that the feeding speed of the seedlings is synchronized with taking seedling action of the planting holding device. The conveyor belt is used to transport the seedlings, and the conveyor belt was designed to send seedlings at a speed of 40 plants per minute. Using a compression matrix for field planting functional verification tests, the average plant spacing is 98.6 cm when the transplanter moves at a stable speed of 2.1-2.6 km/h. The pass rate of the plant spacing is 90.62% and the lodging rate is 21.9% which is slightly higher. In the follow-up study, dual-ground-wheel driving would be used to improve the reliability of the transmission and obtain uniform spacing; a hole shape with the same level and the same depth should be acquired, and the lodging rate after the landing of pie-shaped matrix would be reduced by increasing the copying mechanism and optimizing the shape and structural parameters of the hole puncher.