Abstract: Biotic fitness of both resistant and susceptible strains of Plutella xylostella to abamectin was investigated in laboratory. Results showed that there was no reproductive disadvantage in the resistant strain (ABM-R). Moreover, the mating rate, hatchability, and effective oviposition index of ABM-R were significantly higher than that of the susceptible strain (ABM-S). The intrinsic rate of increase of ABM-R was 0.139, which was 1.19-fold compared with that of the ABM-S strain, and its relative fitness was 1.49 times that of the ABM-S. The life-table of the two strains was established. And the strategies of resistance management were also discussed.