Abstract: The result of this experiment showed that the critical surface tension needed by rice, wheat and wild cabbage leaves was 36.7, 36.9 and 36.4 mN/m respectively. Furthermore, the surfactant did not provide the necessary critical micelle concentration in the spray liquid of conventional concentration of most insecticides. 30 insecticides were measured in laboratory and the surface tension of the liquid was much larger than the needed critical surface tension of rice, wheat and wild cabbage leaves, which caused the difficulty in wet-spreading of the insecticides on these leaf surface.