Abstract: In view of 3D coordinate transformation nonlinear model,in order to adapt direct search method to solve the transformation parameters,it is necessary to make the model simple and operand small by way of two step measurements as follows.One is to transform the 7 parameters model to 4 parameters model by eliminating translation 3 parameters;the other is to replace 3 rotation angles of rotation matrix with antisymmetric matrix 3 independent elements.A kind of direct search method which integrates genetic algorithm and pattern search method is used to solve the transformation parameters;and it is suitable to rotation of random angle.The example indicates the algorithm is feasible.Lastly,for some factors effecting coordinate transformation precision,some conclusions are made by analysis,including the higher coordinate precision of original point of baseline vector model the better coordinate transformation precision and 3-5 common points are fit to solve the parameters.