The preparation techniques of slow/controlled-release fertilizers films with hogwash oil as the starting material was studied.Six coated urea were prepared through solid-liquid reaction,and their controlled-release capability of nitrogen was researched with water dissolution.Results showed that the maximum recovery rate of hogwash oil can be obtained by addition of sulphuric acid 2.6%,water 40%,and then water washing six times.Sulphuric acid is more economic than phosphate acid.Alcoholysis hogwash oil with suitable viscosity and hydroxyl value can be got when hogwash oil reacts with polyisocyanate (mole ratio (1.0∶0.7)-(1.0∶0.9));The characteristic films made from prepolymer of alcoholysis hogwash oil and polyisocyanate with bentonite were determined by nitrogen transiting dose of the saturated urea solution,and the membrane permeability was increased along with the proportion of alcoholysis hogwash oil.Six coated urea with well controlled-release effect for water dissolution rate could be produced along with two kind hydroxyl value alcoholysis hogwash oil and two ratio of hogwash oil to polyisocyanate (mass ratio:2.5∶1.0 and 3.0∶1.0),the dissolution rate in water is 8.9%-11.1% in 24 h,seven days cumulate ones is 35.7%-42.1%.