The invention provides a purification and expanding propagation method for propylaea japonica. The method comprises the steps that 1, the propylaea japonica is fed in an insect feeding cage, wherein horsebean seedlings are planted and enough pea aphids are fed in the insect feeding cage, a flowerpot of horsebean seedling planting is wrapped with a preservative film, and the number of the stretching blades of the horsebean seedlings is as little as possible so that most of spawn is spawned on the preservative film; 2, the spawned preservative film is collected, and larvae are hatched in a warm and humid condition; 3, the larvae are taken out in time and put into another insect feeding cage to be fed, after the larvae pupate, the spawn collecting operation in the step 2 is stopped; 4, after the spawn in another insect feeding cage in the step 3 is collected through the preservative film, the step 2, the step 3 and the step 4 are repeated until five generations, and the purified spawn is obtained; 5, after the purified spawn is hatched, expanding propagation in the insect feeding cage is conducted. The purification and expanding propagation method is beneficial to purify the generation number of propylaea japonica in the field and reduce newly hatched larvae and imagoes feeding of the spawn indoors, the operation is easy, the cost is low, and purification and expanding propagation for propylaea japonica indoors can be completed effectively.