Abstract: Fuzzy saaemble analysis was used to separate and classify 3 kinds of the symptom-varies in white rust of dwamp morningglory which comes from last every week of infect period in 1984/1989. The results show that the method can be used to classify symptom-varies according to 4 kinds of the similarities in last every week, including temperature on leafage, rainfall, disease index, and cloudy days ect. and its conicidental ratio with actual disease index on this week is 88.6%.The paper also deals with the option on the optimum rate of fungicides under constraint condition, with the equation constraint a general principle of alternative optimum rate of fungicides is derived, whereas under unequal constraint condition a nonlinear programming is tried so as to find out the optimum solution. With regard to the quadratic function of metalaxyl application a method of calculation on optimum solution is also given.