To obtain a full-scale assessment of the influences of transgenic Bt crops on the beet armyworm, Spodoptera exigua (Hübner), larval development and adult reproduction of the S. exigua were examined when early-instar larvae fed on artificial diet containing different concentrations of Cry1Ac toxin for six days and then transferred to non-Cry1Ac toxic diet. The results showed that the corrected mortality of S. exigua significantly increased with increasing of concentration of Cry1Ac toxin and prolonging of feeding time when early-instar larvae fed on artificial diet containing Cry1Ac toxin for six days. As compared to the control fed on non&amp;#57361;Cry1Ac toxic diet, larval body weight was significantly decreased when early-instar larvae fed on the artificial diet containing Cry1Ac toxin. Larval duration, pre-pupal duration, male and female pupal duration were all significantly delayed, but male and female pupal body weight were not significantly different from those of control. Percentage of pupation was significantly declined, but the emergence rates were not significantly different from those of control. Pre-oviposition period of adult was significantly delayed, but oviposition period was not significantly different from that of control except that adults with early-instar larvae fed on the 5 &amp;#956;g/g Cry1Ac toxin diet had a significantly longer oviposition period (1.3 d longer). The highest number of eggs laid per female was observed when the early-instar larvae fed on the artificial diet containing 10 &amp;#956;g/g Cry1Ac toxin, but all the Cry1Ac toxin diet treatments had no significant difference compared with the control. Female longevity was all significantly prolonged, but not male except the treatment of the highest concentration (80 &amp;#956;g/g) of Cry1Ac toxin diet which resulted in a significantly longer longevity (2.4 d longer). These results indicated that the artificial diet containing different concentrations of Cry1Ac toxin have significant inhibition on the growth and development of S. exigua or directly resulted in death in larval stage, but when larvae were transferred to non-Cry1Ac toxic diet, they could recover fast, pupate, emerge and oviposit successfully. Therefore, once the early-instar larvae could survive and complete a generation after eating the plant tissue expressing Cry1Ac protein in the late development of the transgenic Bt crops, this will bring more risk of S. exigua on resistance to Bt crops, so it needs to develop an appropriate management strategy for this pest in agricultural Bt crops ecosystem.