Abstract: Abstract: Currently, researches both in domestic and oversea on fruit harvesting machine mainly focus on vibrating type, and making fruit separated from plants through vibration. Most of the related studies and reports of fruit harvesting machine are aimed at recovery efficiency, while the studies of small berries collecting and transportation are still relatively rare. In order to solve harvesting problem of small berry and figure out transmission characteristics of the air-suction conveying equipment, especially to get the best dimension of the conveying pipe diameter, this paper attempts to optimize the parameters of small berries collecting conveyer with blackcurrant (broad variety) as the research object, and thus confirms the optimal diameter size of the pipeline. First of all, based on the physical properties of the fruit blackcurrant, the suspended velocity is about 5 m/s by resorting to aerodynamic and other related theory. In order to prevent blackcurrant fruit movement from being too fast to fracture, the maximum wind speed is about 73 m/s by means of analyzing and calculating. Therefore, the suitable wind speed range of blackcurrant fruit movement in the conveying pipe is nearly 5-73 m/s. Secondly, using coupling EDEM- FLUENT software for modeling and simulation of conveying equipment, the gas pressure contours of 3 kinds of conveying pipes with different national standard diameter were analyzed, and it was concluded that air pressure inside the pipeline reduced gradually with the air flow direction. Through calculating the pressure drop to compare the conveying efficiency of 3 kinds of pipelines with different diameter, the pressure drop of ?40 pipe was larger than the remaining pipes, which meant that the ?40 pipe had a higher transmission efficiency than the remaining pipes in the same flow. According to the results, the value of the maximum force for the ?40 pipe which broke through critical point was less than the remaining pipes during the process of conveying, and the fruit breaking rate of the ?40 pipe was low using the software to monitor the maximum force of blackcurrant fruit in the conveying pipe. Finally, we designed and made the experimental device of blackcurrant collecting and transmission. The conveying efficiency and fruit breaking rate of 3 kinds of pipelines were tested under different gas flow, and the test results were statistically analyzed. With the increase of gas flow, the conveying efficiency and fruit breaking rate of 3 kinds of pipelines accordingly increased. Under the same gas flow, the transmission efficiency of ?40 pipe is high. When the flow increased, the transmission efficiency grew rapidly. When the gas flow rate increased, only the growth rate of fruit breaking rate of ?40 pipe gradually slowed. The regression equation of conveying efficiency and fruit breaking rate with the flow conformed to the law of quadratic curve and the regression coefficient was greater than 0.9. The result presents that the best inside diameter of pipeline is 40 mm, and the conclusion also provides the reference for research and development of other small berry picking machines.