Abstract: Inertial navigation system fine alignment based on Kalman filter is normally carried out under navigation frame.Earth-centered-earth-fixed(ECEF) frame is an important frame for combination navigation and inertial geodesy but no previous research has been shown for the fine alignment under this frame.Beginsing from mathematical deduction of a 12-states Kalman filter equation under ECEF frame,we estimate the misalignment angles and determine the transformation matrix from body frame to ECEF frame for the fine alignment.A simulation calculation is accomplished for this algorithm to prove its validity and availability.Besides,the alignment accuracy is also discussed.Experimental results show that the fine alignment can also be done under ECEF frame for inertial navigation system.