A field experiment including five treatments, they were CK(neither urea nor chicken manure was applied), N₁₀₀(100% of nitrogen was provided by urea), M₁₀N₉₀(10% and 90% of nitrogen was provided by monosodium glutamate wastewater and urea, respectively), M₃₀N₇₀(30% and 70% of nitrogen was provided by monosodium glutamate wastewater and urea, respectively), and M₅₀N₅₀(50% and 50% of nitrogen was provided by monosodium glutamate wastewater and urea, respectively) was performed. The experiment was to evaluate the effect of monosodium glutamate wastewater co-applied with inorganic fertilizer on soil microbial biomass carbon(MBC) and microbial biomass nitrogen(MBN) contents in the rhizosphere soil of watermelon. The results showed that using monosodium glutamate wastewater can accelerate soil biological processes, and was of great advantage to the transformation of organic matter and provision of nutrition to meet the needs of watermelon's regular growth. The dynamic changes of MBC and MBN contents were different at different growth duration. Compared to the M₃₀N₇₀ treatment, the M₁₀N₉₀ and M₅₀N₅₀ treatments had less effect on MBC and MBN contents in the watermelon rhizosphere soil. In conclusion, monosodium glutamate wastewater co-applied with inorganic fertilizer, especially the M₃₀N₇₀ treatment, could improve the ecological environment of watermelon rhizosphere soil and could balance nitrogen alimentation.