This paper presents a parametric optimization approach to solve reentry guidance. Due to the various constraints imposed on the trajectory, original guidance problem can be converted into an optimal control problem with a merit function to be minimized. Direct implementation is too complex to get a reasonable result, while a numerical parametric optimization approach is feasible and efficient if we choose appropriate control variables as the optimization parameters and effective optimization algorithm. This paper converts all the constraints into a penalty function, and parameterizes the control variable in infinite-dimension to transform the reentry guidance to an infinite-dimension parametric optimization problem. Simulation result reveals that, the penalty function divergence to the pre-set threshold after 26 iterations and 301 calculation of penalty function.