Abstract: In this paper, we study and discuss the precision of the calculation of ocean loading effects (M2). Error models are developed for both synthetic and separated cases. The precisions are estimated of the calculation of ocean (M2) effects on gravity, tilt and strain in the China mainland. The results show that the precision are noticeably affected by the earth models and ocean maps, especially by the difference between the chosen earth models. The nearer to the ocean, the lower the relative precision. Finally, the present study of loading and the problem of correction precision are investigated and evaluated.