The invention discloses a navigation method of a pickaback guided rocket projectile based on an MIMU. The navigation method comprises the following steps: performing initial alignment on a navigation system, and solving a pitching angle and a roll angle of the rocket projectile at the initial moment through a self-aligned manner; performing navigation solution initialization for providing system initial attitude, position and speed for an inertial navigation solution part; updating the system attitude through an attitude updating algorithm to obtain real time attitude information of the rocket projectile; updating system speed and position through a speed and position updating algorithm to obtain real time speed and position information of the rocket projectile. According to the navigation method, under a transmission coordinate system, strap-down inertial navigation solution is carried out, and positioning equipment and attitude determination equipment are not needed to be additionally mounted on a rocket projectile base, so that the cost is reduced, and the accuracy is improved.