Three-axis orthogonal gyro installation in strapdown inertial navigation system can only perform limited reliability as single gyro fault can directly lead to the whole system fault, and navigation error can be quickly accumulated with time increasing due to its own mechanism. To solve these problems, a single-axis rotational modulation SINS method based on hexagonal pyramid redundant configuration is presented. An optimization criterion of redundancy configuration for multiple index constraints is established, and a hexagonal pyramidal configuration scheme is designed. And the single-axis rotation method is introduced to modulate the equivalent gyro drift in the vertical direction of rotary axis. Simulation results show that the proposed method could significantly improve the reliability and accuracy of SINS.