Gravitational acceleration measuring method and system suitable for strapdown inertial navigation system

The invention discloses a gravitational acceleration measuring method and system suitable for a strapdown inertial navigation system. The gravitational acceleration measuring method comprises the following steps: step 1, rotating an indexing mechanism to a first position; 2, under the static measurement condition, obtaining n1 original data of a first position through samplingby an X-direction accelerometer, a Y-direction accelerometer and a Z-direction accelerometer; 3, rotating the indexing mechanism by 180 degrees around the horizontal axis to a second position; 4, under the static measurement condition, obtaining n2 original data of a second position through sampling by the X-direction accelerometer, Y-direction accelerometer and Z-direction accelerometer; and 5, performing calculation based on the original data obtained in the step 2 and the step 4, and outputting a gravitational acceleration value g. According to the invention, the indexing mechanism embedded in the strapdown inertial navigation system