With calculation of phase match parameters and effective nonlinear coefficients, several different nonlinear optical processes using one biaxial crystal KTiOPO4 are considered. The nonlinear optical processes include (1) SHG (type II) of 1.064~0.532m, (2)SFG of 1.064+0.6~0.383m,(3)DFG of 1.064~0.6-1.375m