Soil microbial biomass carbon and nitrogen are the important indicators to study soil fertility, soil nutrient transformation and circulation, and environmental changes. During this research, the seasonal dynamics of soil microbial biomass C and N contents and their relation with the changes of soil nutrients content in Ulmus pumila forest[25 years old (UPM), 10 years old (UP)], Robinia pseudoacacia forest (RP), Fraxinus chinensis forest (FC), Populus popularis forest (PP), P.×liaoningensis forest (PL), mixed forest of P.×liaoningensis and R. pseudoacacia (PR) and CK (naturally occurring shrub-grassland) were investigated. The purpose of this study is to provide a scientific basis for selection of coastal shelterbelt tree species and forest management in this area. The results showed that soil microbial biomass increased significantly by afforestation. Among all the forest types, UPM has the highest soil microbial biomass C and N contents, which are 2.50 and 2.09 times than CK. The microbial biomass C and N contents in soil layer of 0-10 cm were larger than those in 10-30 cm soil layer, and the seasonal dynamic change of soil microbial biomass in two soil layers varied significant differently. In the 0-10 cm soil layer, the seasonal dynamics of soil microbial biomass C and N contents in the typical shelterbelts on Bohai muddy coast were higher in spring and autumn, and lower in summer, with a "V" shape trend. The change trend of soil microbial biomass C in the typical shelterbelt under 10-30 cm soil layer was consistent with that of 0-10 cm soil layer, which showed a lower in summer, and a higher in spring and autumn, also with a "V" shape trend. There are mainly three forms of microbial biomass N variation:"V", inverted "V", and straight line. In the 0-30 cm soil layer, the average contribution rates of soil microbial biomass C to soil organic carbon in UPM, RP, FC, PP, PR, UP, PL, and naturally occurring shrub-grassland were 1.59%, 1.68%, 1.42%, 1.54%, 2.29%, 1.80%, 2.02%, and 1.12%, respectively, and in the 0-30 cm soil layer, the contribution rates of soil microbial biomass N to soil total nitrogen were 1.85%, 1.30%, 1.08%, 1.35%, 2.49%, 1.57%, 2.08%, and 2.32%, respectively. The correlation of soil microbial biomass C and N in all forest types were significantly positive, and soil microbial biomass C and N had significantly positive correlation with soil total nitrogen and organic matter, and had significantly negative correlation with soil conductivity. In addition, soil microbial biomass C had significantly positive correlation with soil available P. From the results of seasonal dynamics of microbial biomass C and N in different soil layers, it could be drew the conclusion that microbial biomass increased by afforestation in muddy coastal soil, but ground water was rose in summer, accompanied by the increment of salt and alkali content, moreover, trees utilize large quantities of nutrients to maintain growth, thus, the soil microbial biomass was lower. Based on the comparison of soil microbial biomass C and N content and their contributions to soil N pools among all forest types, the conclusion can be made that UPM and PR are the most conducive tree species to the recovery of soil microbial function and nutrient fixation on the Bohai muddy coast.