The Uniformity of standard orthogonal design is improved by differential evolution method . Standard orthogonal design and Improved orthogonal design are used respectively in transition trajectory optimization design of suborbital launch vehicle. In case of the same sampling size, The estimation error of the regressive model based on standard orthogonal design can meet the precision requirement, and the regressive model based on improved orthogonal design can reduce the estimation error more than the premier model. Complex optimization method is used to search the optimization point of the two models, and the result based on the two models are both meet the demand of precision, while the result of the model based on improved orthogonal design has better optimization effect. The improved orthogonal design method increases the sampling efficiency and it is a effective method applying in optimization design of trajectory.