A Compressible thin-layer Navier-stokes solver is developed based on the flux vector splitting method to investigate 3-D flow field of forced deflection nozzle(FDN). 3-D grid generation is accomplished by solving Possion Equation. The Block-Line-Gauss-Siedel relaxation approach is employed to solve the discretization equations with upwind scheme. Numerical results show that FDN is of the ability to compensate the variation of environmental pressure automatically.. Firing test experimental study is also conducted for FDN which proves that FDN is feasible and effective. Numerical and experimental results about FDN pressure distribution are in quite good agreement.