The experiment was carried out on cultivation patterns of winter wheat and summer corn in Huantai County, Shandong Province, China. The purpose of the study was to understand how soil fertility maintaining practices, such as chemical fertilizer application level, the use of organic fertilizers and the return of crop straw to the field affected the dynamics of soil microbial biomass carbon (MBC) content in a high production agro-ecosystem of northern China. Ten treatments of fertility maintaining practices in the field were chosen (where the symbol “+" means combination application): ①wheat straw + corn straw, ②wheat straw, ③wheat straw + corn straw + chemical fertilizer1 (600kgN/(hm²•a)), ④wheat straw + chemical fertilizer1, ⑤wheat straw + corn straw + chemical fertilizer2 (480kgN/(hm²•a)), ⑥wheat straw + chemical fertilizer2, ⑦wheat straw + corn straw + chemical fertilizer3 (720kgN/(hm²•a)), ⑧wheat straw + chemical fertilizer3, ⑨wheat straw + corn straw + chemical fertilizer1 + organic manure, and ⑩chemical fertilizer1 randomly designed and applied in the experimental plots. The content of soil MBC was measured in the different crop growth stages in laboratory. The results showed that: the content of MBC was highly impacted by the intensity of organic material input and had an ascending trend with organic material. A single chemical fertilizer application could restrain microbial activity in high production agro-ecosystem, although the restraining action was weakened by the input of organic material. An equal content of MBC was found in the plots where different fertilizer levels were combined with crop straw. Corn straw and wheat straw return to the field cooperating chemical fertilizer could significantly weak suppressive effect of chemical fertilizer to microbial activity. Organic manure application had an obvious impact on MBC concentration. Different combinations of straw (wheat straw + corn straw and wheat straw) returned to the field had distinct variation in different seasons. Further, the content of MBC in corn straw and wheat straw return to field was higher than that in wheat straw return to field from annual average MBC. The content of MBC had the following ascending trend as concerning annual average MBC: Chemical Fertilizer1< Wheat Straw + Chemical Fertilizer1< Wheat Straw + Chemical Fertilizer2 < Wheat Straw + Corn Straw + Chemical Fertilizer2 < Wheat Straw + Chemical Fertilizer3 < Wheat Straw + Corn Straw + Chemical Fertilizer1 < Wheat Straw + Corn Straw + Chemical Fertilizer3 < Wheat Straw < Wheat Straw + Corn Straw < Wheat Straw + Corn Straw + Chemical Fertilizer1 + Organic Fertilizer. This suggested that for a high fertility agro-ecosystem the best soil fertility maintaining practices was that of returning straw to field with organic manure