Abstract: The result of path analysis shows that the ecological factors affecting characters and the yield of summer wheat are daily mean temperatures during the filling period and the whole growing season.The test of the sigrificance of yield difference at different eltitudes indicates:The optimum area for Summer-sown wheat is on Zhang Jiakou Baxia hilly region,its altitude is 1200 M above sea level.In this area,the daily mean temperature is 14.7-19.8℃ during the growing season and 13-6-19.2℃ in the filling period.The relationship of regression coefficient between the altitude and daily mean temperature;the yield and its growth charaters shows:when the elevation goes up by 100 M in the range of 800-1800 M,the daily temperature lowers 0.9-0.8 ℃,the yield per mu,the weight of 1000 seeds and the plant height in-crease 14.1 kg,0.54 g and 3.7 CM respectively.A two-factor analysis of variance between the cultivars sowing time and yield at different altitudes indicates that in Yu county which is located at 39°50’north latitude the most suitable cultivar is Zhuocheng 1,then Cong 17 and Zhong 7606;the optimal sowing time is the later half of June at 1200 M altitude,arounde middle of June at 1400 M,the early half of June at 1600 M and in the first ten-day period of June at 1800 M.In Chong Li county of 40°58’north latitude,the most suitable cultivars are Cong 17,then Zhuocheng 1 and Zhong 7606;the optimal sowing time is in the later half of May at 1200 M,around the middle of May at 1400-1600 M,and in the last ten-day period of May at 1800M.Compared to Yu county,Chong Li county is one degree to the north,so the sowing time should be 20 days earlier.The mature period of wheat is in September.But,the sowing time at different latitudes and altitudes depends on the local temperature.

Key words: Wheat, Summer-sown, Daily mean-temperature