By combining advantages of S_N method (high calculational efficiency) and advantages of MC method (fine geometrical modelling), three-dimensional discrete ordinates-Monte Carlo method (3D S_N-MC coupling method) is able to calculate cavity streaming dose rate in short time. S_N-MC coupling method is applied on Qinshan No.1 reactor and CAP1400 reactor cavity streaming calculation. Results of S_N-MC coupling method are compared with measurements and results of MCNP bootstrapping method. It shows that theoretical model and codes of 3D S_N-MC coupling method are both correct.