Abstract: In order to explore the law of photosynthetic active radiation in winter sunlight greenhouse of Panjin and serve the region agricultural facilities better, based on the observed data of sunlight greenhouse microclimate and of the nearby weather station during winter in 2012, the methods of correlation analysis and stepwise regression analysis were adopted to study characteristics of photosynthetic active radiation in sunlight greenhouse and the ratio of photosynthetic active radiation to global radiation under different weather types during winter, and to set up forecast models of photosynthetic active radiation in sunlight greenhouse under different weather types during winter. The results showed that: (1) the daily variation of photosynthetic active radiation in sunlight greenhouse on sunny and cloudy days were both obvious, when it’s cloudy photosynthetic active radiation in sunlight greenhouse was 1-38 W/m2; (2)η PAR on typical cloudy day was the highest, on cloudy day was secondary and on sunny day was the minimum during winter; (3) the methods of stepwise regression analysis were respectively adopted to set up models of the highest daily maximum photosynthetic active radiation, the total daily photosynthetic active radiation, daily maximum global radiation, and the total daily global radiation in sunlight greenhouse associated with climate outside, the models passed the 0.01 level of significance, and fitting test had been carried out: 4 factors were fitted good on sunny and cloudy day, but poor on overcast day.