Abstract: Through simulation, the effect of fenvalerate on red soil urease activity in subtroptical fruit gardens was investigated. The results show that soil urease activity in the first three days is increased and followed by inhibition, after seven days it is lower than the control. The degree of activation and inhibition is directly related with fenvalerate concentration. As the reaction concentration of substrate (urea) is below the saturation, urease activity improves with the increase of urea concentration. The relationship between soil urease activity (U) and urea concentration (C) as well as fenvalerate concentration (C) can be expressed in the given regression model as: U=β₀+β₁×C. This implies that adsorption and desorption are the basic mechanisms of soil reaction catalyzed by urease; that soil fertility is an important element in the relationship between soil urease and fenvaleraten; thus soils with higher fertility amortizes the effect of fenvalerate on soil urease and therefore less affected by fenvalerate.