Many crops have the absorption peak of trace element selenium(Se) in their specific growth period.In order to prepare functional fertilizers matching the release rate of selenium with the absorption rate of crops, the sustained release effect of selenium was evaluated by using polyurethane coated sustained release selenium fertilizer.In this study, water purification experiments were conducted on several kinds of polyurethane selenium fertilizer with different coating quantities at 25℃ and 100℃ to evaluate the sustained release effect of Se element..The results showed that the dissolution rate of Se in fertilizers at 25℃ and 100℃ showed the following laws: the overall trend of the Se release rate in each group was relatively rapid at the beginning, and then tended to be stable, showing three different stages: the rapid release period, linear release period and declining release period. The Se release rates for uncoated Se fertilizer and 2% coated Se fertilizer did not meet the standard of slow-release fertilizer in the early 24 hours, and there was no significant difference between the two groups. The released Se rate for coated fertilizer with 4% and 6% polyurethane could met the standard of sustained-release fertilizer, and the sustained-release period was more than 40 days, and there was no significant difference between the two treatments. The dissolution rate method for Se in fertilizer at 20℃ can be replaced by the more rapid dissolution rate method for Se in water at 100℃.Taking all factors into consideration, 4% coated fertilizer was the optimal solution.