The N₂-fixing capacity of locust nodule was high in neutral, low calcium and weak acid soils, but low in strong acid and strong calcareous soils of the Sichuan Basin of China. The relationship between iocust nitrogen fixation capacity and physico-chemical properties could be expressed by a multivariate regression equation. In course of fitting into the equation the authors advanced the method converting the nonlinear factors into linear ones, and simulated the interaction between the soil's factors with an electronic computer. In 42 forest soils avaifable P, and its interaction with CO₂-biological activity and total P₂O₅ were the main factors,influencing nitrogen fixation, and coordinations between pH and CaCO₃, and total P20s (ineluding available P) and available Mo made important contributions to nitrogen fixation as well. The equation can be applied to evaluate and forecast Na-fixing potential of the symbionts under different soil conditions.