The whole nonlinear optical coefficients of GdCOB crystal are evaluated by phase matching SHG method and Maker fringe method. The spatial distribution of effective nonlinear coefficient d eff are proved with the crystals cut in different directions in the experiments. The results show that d eff reaches the maximum of 1.68 pm/V at the direction of θ=66.8°,φ=132.6°. The SHG conversion efficiency reaches 48% with a 6 mm long GdCOB crystal cut along this direction.