Abstract: During two harvests of one year in Huanghuai Plain, Summer soybeans are alternated for 1~4 years, the incidence of pods without peas per plant increaces 8.8~35.3 per cent;The soybeans'yield reduces 12.1%~44.9%;There is an obvious positive correlationbetween the incidence ofindividual seedless pod and the year length of alternate cropping, r=0.9895※※;while the incidence of individual seedless podhas notable inverse correlation with the yield, r=-0.9945※※.Summer soybeans are alternated by adding one year, the rate of individual seedless pods increases about8.8%;While the rate of individual seedless pods increasesby per 1%,soybeans'yield drops about 43.6kg/hm2.The biological effects of alternatecropping which cause pods without peas and yield reduction are as follow: lowness of plant height, efficient branches, reduction of individual pods' number and seed weight, drop of 100-seed weight; Bad variation of soil micrpflora, Those fungoid diseases such as root, downey mildew and gray speck of soybean become more serious ;Those minim nutritive elements' contents wane obviously ,such as quickly availablephosphor, Kalium Potass, Boron ,etc;Root's growth suffocate, root vigor drops. here are the prevententive measures: Reasonableirrigation and drainage. Choices of anti-alternate cropping' s good seeds such as Shang soybean 1009,etc;Balanced use of N、P、K、Boron fertilizers; Use of plant growth Regulators; Prevention of pests and plant diseases, etc.