Load structure method is commonly used in tunnel design; there are two problems for its implementation in Marc software: first, the force cannot be applied directly in Marc; second, the position of the spring around the tunnel is unknown. In view of first problem, by means of force conversion, a subroutine programming with Fortran is adopted to exert the force. For the second problem, iterative algorithm is adopted; the tension spring will exit calculation, and a comparison of the spring position in the two steps will be made, if the position is the same, the computation will finish. The work above realizes the Load structure method in Marc software and enlarges the application of Marc software in underground engineering. The verification example is given to prove the validity of the interface subroutine.