Abstract: In order to explore the toxicity of hebicides on soil microorganisms, the nitrogen transformation of microorganisms in fluvo-aquic soil and the respiration intensity of microorganisms in krasnozem, brown soil and fluvo-aquic soil were determined after exposure to sulfometuron methyl and clodinafop-propargyl, respectively. The soils were treated with these herbicides at the recommended field concentration (RFC), 10 and 100-fold of RFC and then incubated for 15 days. In terms of sulfometuron methyl, the inhibition of respiration was abserved in the exposed brown soil, whereas soil respiration intensity was significantly increased in fluvo-aquic soil. In krasnozem, soil respiration was inhibited after the exposure to sulfometuron methyl in 10 fold application rate treatment, but it was stimulated in the other two treatments. With regards of clodinafop-propargyl, the results indicated that respiration were inhibited in krasnozem and brown soils, but it was stimulated in fluvo-aquic soil. Regarding to nitrogen transformation, sulfometuron methyl significantly increased the NO3--N contents of the fluvo-aquic soil after the exposure to the recommended field concentration (RFC) and 5-fold of RFC for 7, 14, 28, 42, 56 and 70 d, respectively. The NO3--N contents was significantly increased 28 d after the exposure to clodinafop-propargy. However, no significant change between the control and the treatment group was observed 0, 7, 14 and 42d after the exposure. In summary, sulfometuron methyl and clodinafop-propargyl showed low toxicity to soil respiration intensity in the three soils, and no long-term effects on nitrogen transformation were observed in the fluvo-aquic soil.