Abstract: In order to understand the current situation and development of resistance of field population of diamondback moth, Plutella xylostella (L.) to chlorantraniliprole in Yunnan Province, the sensitivity of three diamondback moth population from Tonghai County of central Yunnan, Midu County of west Yunnan and Linxiang district of southwest Yunnan to chlorantraniliprole were determined by the leaf dipping method. Meanwhile, synergism effects of triphenyl phosphate (TPP), piperoayl butoxide(PBO) and diethyl maleate (DEM) to the F1 generation of Tonghai population were tested. The results showed that the resistance levels of Tonghai population of P. xylostella to chlorantraniliprole showed a tendency of going up yearly, with resistance index increased from 2.30 in 2009 to 47.79 in 2012, and to 43.05 in 2013, which reached middle level of resistance; Midu population of P. xylostella showed low level resistance except in 2010 when the resistance index was 12.35; Linxiang population of P. xylostella showed low level of resistance, with resistance index remained between 1.01-4.60 during 2009—2013. t The three compounds had no significant synergistic effects on the toxicity of chlorantraniliprole to P. xylostella.