ISAR imaging has been the focus in recent years. Based on Doppler, the one-dimensional imaging is obtained. Through range alignment and auto-focus, the target can be equivalent to a rotation model. Based on the rotation model, the movement of the ship target will be divided into a horizontal component and a moving component. The first one is useless in the ISAR imaging, so it must be compensated. This is the important step. Based on the rotation model, for the moving smoothly ship, the two-dimensional ISAR imaging can be got through range alignment and auto-focus. But the apriori knowledge of ship target motion is generally unknown, because of their uncooperative moving, the echoes have an obvious time-variant character. Based on the periodicity of Doppler frequency, the whole dwell time is divided into several intervals, then, based on the above, the instantaneous ISAR imaging of every time interval can be got and simulations are done to verify the method. The verification result shows that the method is effective for the non-stationary ship imaging.