Abstract: In this paper， we studied the effect of various concentrations of potassium dihydrogen phosphate and potassium humate on photosynthetic characteristics， activity of antioxidant enzymes and yeild of late rice in heading and flowering period when autumn low temperature was coming. The results were as follows: （1） The photosynthetic capacity of rice， chlorophyll a， chlorophyll b and carotenoid content increased under different fertilizer treatments ，which foliar spray of 0.3% potassium dihydrogen phosphate and 0.03% potassium humate had notable experimental effect on resistance to low temperature. （2） Peroxidase， superoxide dismutase and catalase activity and malondialdehyde content gradually increased under the effect of autumn low temperature. The sensitivity of SOD and CAT were very strong to fertilization treatments， but for POD， it was relatively weak. The content of MDA was decreased in different degrees. And the increase of the 3 protective enzymes was the largest， and the content of MDA was the least under the processing of 0.3% potassium dihydrogen phosphate and 0.03% potassium humate. （3） The 1 000grain weight and seed setting rate were higher than the control under the processing of 0.3% potassium dihydrogen phosphate and 0.03% potassium humate， which resulted in a significant increase of production; However， the yield traits were slightly inhibited by 0.05% potassium humate. （4） The correlations between 1 000grain weight， seed setting rate and activities of SOD， POD， CAT， MDA content were significant， and all of these traits were significant with yield except plant height and tiller number. The conclusions could provide certain theoretical basis for production forecast.

Key words: cold dews wind, late rice, heading and flowering period, potassium fertilizer, photosynthetic characteristics, yield