【Objective】 To study the biological activity of azadirachtin-rich dry powder, azadirachtin A and azadirachtin B, and establish a method for determinating azadirachtin content of dry powder.【Method】 Azadirachtin-rich dry powder was prepared by ethyl acetate extraction method, the azadirachtin content of dry powder was determined by HPLC and the biological activity was measured by leaf disc test. 【Result】AFC₅₀ of zadirachtin-rich dry powder was 0.28 μg·mL^-1 against 2nd instar larvae of Spodoptera litura and 70.71 μg·mL^-1 against the 3rd instar larvae of Pieris brassicae 24 h after treatment. The antifeedant activity of azadirachtin-rich dry powder was clearly higher than that of azadirachtin A and azadirachtin B. 【Conclusion】 This preparation method of the dry powder is simple, effective, and has good biological activity. It is recommended for popularization and application.