In this paper, by using the idea of the aggregate function method, a new aggregate homotopy method is proposed to solve the nonlinear complementarity problem (NCP). The homotopy equation is constructed based on the aggregate function which is the smooth approximation to the reformulation of the NCP. An existence condition for a finite homotopy path is derived from the limiting behaviours of the complementarity mapping at infinity. This condition is different from any existing ones in the literature but can be easily verified. The results provide a theoretical basis to develop a new computational method for NCP. The numerical experiment results show the method is effective.