Abstract: In order to identify the suitable sowing date and the key effect meteorological factor, with the main cultivars of sweet sorghum as the tested materials in Manas Region of Xinjiang, the photosynthetic characteristics and meteorological factors were measured, to research the change of photosynthetic characteristics and its relationship with meteorological factors among different sowing dates of sweet sorghum. The results showed that, the change of chlorophyll relative content (SPAD) and photosynthetic rate (Pn) expressed in a single peak curve with the peak at flowering stage, and they decreased gradually after filling stage of sweet sorghum. There were significant differences of SPAD and Pn among different sowing dates (P?0.05). Xingaoliang No.3 and Zaoshu T601 were the main cultivars of sweet sorghum in Manas Region of Xinjiang. With the postponing of sowing date, the SPAD and Pn of Xingaoliang No.3 were all the highest under the sowing date of April 25th, and Zaoshu T601 was the sowing date of May 8th. The results also indicated that, it should be sowed proper early for Xingaoliang No.3, and sowed proper lately for Zaoshu T601. The photosynthetic characteristics were significantly positive correlated with air temperature, and negative with wind speed. The temperature was the key meteorological factor affecting sugar accumulation of sweet sorghum, and the effect of precipitation on photosynthetic characteristics was not obvious.