A method for improving insect resistance of plants, in which dsRNA of insect's gene is expressed in plants by using transgenic technique, and then the interfering RNAs are formed in the plants. The interfering RNAs then enter into insects' bodies after being ingested by the insect that eats the plant, and conduct RNA interference against the target gene, thereby expression of the target gene is suppressed by RNA interference. A new plant-mediated method for improving insect resistance by suppressing the growth of insects by RNA interference mechanism.