Spacecraft optimal rendezvous is studied using nonlinear programming method. A recently developed direct optimization technique is employed, which uses a piecewise polynomial representation for the state and controls, thus converting the optimal control problem into a nonlinear programming one. When using the method, the whole orbit is separated to thrust arcs and non-thrust arcs, then the collocation method is used to produce the constraints of thrust arcs, and state transition matrix is applied to producing the constraints of non-thrust arcs. At last, the simulation of coplanar rendezvous verifies the effectiveness and robustness of the method.