改进文献[1]提出的有限差分计算走时的算法．射线路径也可根据互易性原理求出．模型计算表明该方法精度较高并适用于速度差较大的情形．该算法对层析成像、选前Kirchhoff偏形特是非常有用的． Improved algorithm [1] proposed finite difference method to calculate travel time. Ray path can also be calculated according to the reciprocity principle. The model calculation shows that the method is more accurate and suitable for large speed difference. This algorithm is very useful for tomography, pre-selection Kirchhoff skewness.