Abstract: A resistant strain of Plutella xylostella (L.) with 9.09-fold resistance to chlorantraniliprole was obtained by leaf-dipping method treated for with 10 generations.The result showed that the number of eggs laid per female,larval survival rate,pupation rate,pupal weights,emergence rate,and male longevity were decreased significantly,while the larval period was prolonged,which caused a decline of net reproductive rate,intrinsic rate of increase and relative fitness and a prolonged population doubling time.The results indicated that during the initial stage of chlorantraniliprole treatment,the biological fitness of the chlorantraniliprole resistant strain of P.xylostella was low implying the risk of resistance development of to chlorantraniliprole was relatively low.