The invention provides a rotating modulation based coarse alignment method of a static base inertial navigation system, which is simple and convenient to implement, low in calculation and suitable for the engineering application. The method comprises the steps as follows: step one, double shafts of the rotary type inertial navigation periodically rotate according to a default rotating scheme during a coarse alignment process; step two, an analysis method is adopted in each sampling period of an IMU (inertial measurement unit) to solve an attitude matrix estimation value of the IMU; step three, a direction cosine matrix between a carrier coordinate system and an IMU coordinate system is solved according to an output value of an angular position sensor of a rotating mechanism in each sampling period; step four, an estimation value of a carrier attitude matrix at current sampling moment is solved according to the attitude matrix estimation value of the IMU and the direction cosine matrix between the carrier coordinate system and the IMU coordinate system; and step five, an average value of the carrier attitude matrix estimation values obtained at all moments during the coarse alignment process is solved so as to obtain a final estimation value of the carrier attitude matrix.