不平衡推力迭代法假定条块作用力方向平行于上一条块底滑面，这样可能导致计算结果偏大，使工程偏于不安全，通过对坡体滑块间作用力方向角度的修正，对不平衡推力迭代法做了改进，并在不考虑地震力和考虑地震力的情况下分别进行了公式的推导。针对具体算例，利用改进后的计算公式，在Visual Basic编程的基础上，对具体算例进行了计算，并和改进前的方法做了比较。结果表明：改进后的方法对改进前的方法具有一定程度的修正作用，且改进方法的物理过程更加合理，在具体应用上具有一定的实用性。

In the calculation of unbalanced thrust force using iterative algorithm, the inter-slice force direction is assumed to be parallel to the sliding surface of the upper slice bottom, which results in excessive calculation value and leads to danger of projects. The authors improved the method through correcting the  angle between the directions of inter-slice forces in the slope. What’s more, we derived the formulas respectively in the presence of and in the absence of seismic force. On the basis of Visual Basic programming, we applied the improved formula to the calculation of an example and compared the result with that of the previous unimproved formula. The result indicates that the improved method is practicable, and presents a more reasonable physical process.