Abstract: Abstract: The double-factors randomized block design was applied to find out the nutrient release characteristics of multi-layer coated urea, which were coated with water soluble resin (a mixture of vinyl chloride acrylate and vinylidene chloride acrylate) as the primary coating material and C9 modified petroleum resin as the subsidiary material. So 12 coated ureas were prepared as 12 treatments that were made through a fluid-coating technique, that were accompanied with a factor of modified C9 petroleum resin as the inner protection layer with 3 levels of 5, 10, and 15 g per square meter of the kernel fertilizer surface, and another factor of water soluble resin as the middle coated layer with 4 levels of 30, 40, 50, and 60 g per square meter of the kernel fertilizer surface. In addition all coated urea had an outer layer of 10 g C9 modified petroleum resin per square meter of the kernelfertilizer surface. After that, nitrogen release from coated urea was tested, which were in static pure water under a constant temperature of 25℃ with fertilizer and water ratio of 1 vs 5, and further a Richards function was applied to describe nitrogen release, then the result was tested and parameters calculated were used to evaluate the release characteristics of coated urea with different coating materials. Therefore, the aim was to offer some theoretical foundation for the improvement and development of manufacture technology of multi-layer coated urea and its scientific application. The results were as follows. First, it was estimated that there existed 10 sigmoid curves in 12 nutrient release curves through the shape parameter of the Richards function, it was deduced that their release curve may be sigmoid that was coated with water soluble resin and modified C9 petroleum resin. Secondly, it found that the modified C9 petroleum resin inner layer mainly induced action on the curve shape, and the curve shape would tend to sigmoid when the inner layer added from 5 to 10 g/m2. Meanwhile the time of maximum nutrient release speed was delayed by 22.6, 49.3, 74.9, and 39.4 d. Then it increased to 15 g/m2 further, the shape of curve was not varied that the time of max nutrient release speed had not moved or only was brought forward lightly. Thirdly, it showed that a water soluble resin coating layer played a significant role in the nutrient release rate, the longevity was significantly increased with the thickness of middle coated layer added, with that the coating material from 30 added to 60 g/m2 by a step of 10 g/m2, and the range of longevity was definitely between 75.0 and 287.1 d. In summary, the water soluble resin coated urea with a protection layer of water-insoluble material was achievable to release nutrients according to sigmoid. And then multi-layer coated urea could be made with a inner layer of 5 to 10 g/m2 C9 modified petroleum resin, a outer layer of 10 g/m2 C9 modified petroleum resin, and with from 30 to 60 g/m2 water soluble resin coating material, with the products achieving longevity of from 75.0 to 287.1 d, and those products complied with the relevant national standards of controlled release fertilizer.