Abstract: In order to effectively control and reduce the economic losses caused by Plutella xylostella, the effects of sublethal concentration of deltamethrin on the growth and reproductive ability of Plutella xylostella were measured by the drop injection method, and the chronotoxicity of deltamethrin on Plutella xylostella was detected. The results show that the larval survival and adult life of male and female of Plutella xylostella were significantly decreased after treatment with deltamethrin at 12 h LC₃₅ concentration, and the adult emergence rate, pupation rate, hatching rate of Plutella xylostella and daily oviposition number of single female were also significantly declined. Meanwhile, deltamethrin was administered at four different time points zeitgeber times (ZTs): ZT2, ZT8, ZT14, ZT20, which was Beijing time: 6:00, 12:00, 18:00, 24:00 with drop injection method. It was found that the mortality of Plutella xylostella larvae in ZT2 treatment group was as high as 65.97% after 48 hours, while that in ZT20 group was 32.07%. Moreover, the adverse effects of ZT2 treatment group on the larval and adult stages of larvae were significantly higher than those in ZT20 treatment group. In addition, SOD and CAT activities in both treatment groups increased firstly and then decreased, but both were higher than those in the control group, and GST activity showed a downward trend, but the SOD, CAT, and GST activity in ZT20 treatment group were always higher than those in ZT2 treatment group. Therefore, it is suggested that morning application can be selected in agricultural production, which may improve the insecticidal efficiency, indicating that the chronotoxicity should be considered as an important factor in evaluating the insecticidal effects of pesticides. This study provided theoretical basis and support for the control and rational application of pesticides.