Abstract: In order to investigate the effect of organic fertilizer on soil fertility of sycamore trees, this article studied the change of the content of mineral elements of middle size sycamore and microbial quantity of the soil with different treatments of two kinds of organic fertilizers which offered by complete randomized block design, and analyzed the correlation between them. The results showed that: the number of bacteria, fungi, actinomycetes in the soil with the different treatments increased significantly compared to that of CK. And the treatment of TM10-2 (Organic fertilizer of Tianmeile, application of 10 mL per plant, and 2 times of application in total) was the best one among its series. And the TM (Organic fertilizer of Tianmeile) treatments could significantly control the number of fungi; These treatments could significantly increase the content of soil mineral elements, and the treatments of TM10-1 (Organic fertilizer of Tianmeile, application of 10 mL per plant, and 1 time of application in total) and TM10-2 improved the content of macroelement in the soil obviously, while, each of the treatments had no significant effect on calcium and magnesium content in soil. However, the TM treatment series could optimize the ratio of Ca:Mg; As a whole, the TM series in improving available Cu, Fe, Mn content in soil displayed better than that of Z (Organic fertilizer of Zhengen) series; Correlation analysis showed that the relationship between macroelement and the amount of bacteria was extremely significant; and there existed significant correlation between the trace elements and the number of actinomycetes; However, the relationship between either of the two and the amount of fungi were all not significant. According to the results, offering organic fertilizer to urban street trees could significantly improve the soil fertility, and TM fertilizer should be the better one for urban street trees with. And the effect of fertilization was better at its 10 mL per plant level plus 2 times application.