Soy bean 100 seed w eight is influenced by the meteorological co ndi tio n on seed fi llingstag e. The causativ e yield f luctuation is 3. 1% of the to tal output. The w eight of100 seeds dapends upo n mainly o n it s increase rate and i t s co ntinuous time. The increa sera te o f 100 seed weight is mainly inf luenced by the highest temperature, the duration ofsunshine and the rain capacity a t farmer stage. At later stag e i t i s mainly inf luenced bytempera ture diurnal va ria tion and the dura tion o f sunshine. The co ntinuous time of 100seeds w eight are mainly influenced by the temperature condi tio n o f seed fi lling stag e.The sy nthetic effect o f each meteo rological element decides the w eigh t o f 100 seeds.