Applying NPK fertilizer is an effective way to improve soil fertility. Meanwhile, biochar as good soil amendment has been shown to help soil keep fertility when it is used with organic fertilizer and has received attention as a means to mitigate climate change. However, the understanding of impact and mechanism of those different fertilizers on carbon metabolism and ecological security of soil microbes was very limited. With a poplar plantation in the coastal area of northern Jiangsu as the experimental site, we designed four fertilization treatments, CK (control group), T1 (NPK fertilizers), T2 (biochar+NPK fertilizers), T3 (high level biochar), and analyzed the difference in utilizing different carbon sources under different fertilization treatments, to learn whether biochar would cause changes in soil microbial metabolic activity and carbon source metabolism. Our result showed that soil microbial metabolic activity was in  order of T3>T2>T1>CK, and T3 was significantly higher than CK, indicating high level biochar might imp〖HJ*5〗rove soil microbial metabolic activity significantly. The diversity indexes of microbial carbon source utilization were in order of T3>T2>T1 and CK. Only for the McIntosh index, T3 was significantly higher than CK. In the utilization of six groups of polymers, T3 was higher than CK, which indicated that biochar improved the population of microbes that was in favor of polymer utilization, and it also has the potential to change soil microbial functional diversity. Principal component analysis showed that the increase of the number of components in PCA presented information in a more effective way. Meanwhile, the differences in carbon utilization among the different fertilization regimes were not obvious, which indicated that the functioning of soil microbial community was stable and hard to be changed by shortterm fertilization. Although biochar can improve soil microbial metabolic activity, it is unable to change the functional diversity of the microbes.