Abstract: The present disclosure discloses a latitude-free construction method for a gravity acceleration vector under a swaying base earth system. Firstly, a target function based on output information of an accelerator in a fixed-length sliding window under a swaying base is constructed; secondly, measurement information in a period of time window is used to construct the target function, and gradient descent optimization is used to obtain a rough value of qiib0; and finally, the rough value of qiib0 and an apparent motion of a gravity acceleration vector of an inertial system are used to construct the gravity acceleration vector under the earth coordinate system. The present disclosure makes a key breakthrough for solving the problem of high precision alignment of a ship with unknown latitude under a swaying base.