Abstract: The effects of 20% paclobutrazol·mepiquat chloride micro-emulsion(20% P·M ME),a new plant growth regulator,sprayed at the early double-ridge stage,on lodging resistance and yields of winter wheat were studied. The length and the dry weight per unit length of basal internodes were significantly increased, while both the lodging ratio and inclination angle under field condition were reduced. These effects might be caused by the declining of GAs content and IAA content. All the ear number per hm2, grain number per ear, grains weight were improved,and the yield was increased by 6.2%~28.6%. It was indicated that 20% P·M ME could accelerate grain filling after the mid-milky stage, and the contents GAs and Z+ZR in the whole period of grain development were higher than control. But the content of IAA was lowered in the earlier stage while increased after 18 days after flowering. All the changes of levels of GAs, CTKs and IAA, promotion of source activity and filling rate,stimulation of assimilates exportation from stalks and leaves might be attributed to the effects of 20% P·M ME on yields.