Abstract: For deep-penetration shielding calculation, Monte Carlo（MC） method requires the modeling of a great number of particles to obtain reliable results, thus huge computation time is the main problem of the MC method. Source biasing and weight window technique effectively decrease the tally error of deep penetration problem. This paper studies the 3D Discrete Ordinate（SN）-MC hybrid method, generates source biasing factors and weight window parameters for the MC method by using the adjoint fluence rates of the SN method, develops source sampling subroutine for MCNP, and verifies the hybrid method in the measurements in Qinshan Nuclear Power Plant I. The method is then applied in the calculation of CAP1400 reactor pressure vessel fast neutron fluence rate. Numerical results show that 3D SN-MC hybrid method increases the calculation efficiency by 1 to 2 orders for deep-penetration shielding calculation with high precision compared with unbiased MC method.