对隧道断面轮廓线、平曲线的几何特性进行分析，重点对平曲线中的直线、圆曲线、缓和曲线进行了研究，针对这三种曲线用CASIO fx-4800计算器编写了相应的坐标反算程序，根据该反算程序计算出里程和偏距，再结合隧道断面超欠挖程序，可精确地进行隧道放样和检查。该方法也可应用到隧道其他结构的放样和检查上。

Based on the analysis of the geometric characteristics of the contour line and plan curve of tunnel crosssections, the author makes further study on the straight line, circular curve and transition curve of the plan curve. Then, the author works out a coordinate back calculation program for those 3 curves by CASIO fx4800 calculator. The mileage and deviation distance are calculated by the mentioned back calculation program. On basis of the calculation program for the overbreak and underbreak, accurate settingout and checking of the tunnel can be performed. This method can also be used for the settingout and checking of other structures of tunnels.