Abstract: There are four different tidal correction formulas. Fach of them defined a different gravity system. In this paper, the author discussed the problem of inconsistency of gravity determination results (or networks) caused by different tidal correction formulas, and calculated the effects of different tidal correction, formulas on absolute gravity determination, on relative gravity determination, on calibration of the linear constant of LCR-G meter's interval faetor, on calibration of circular errors of LCR-G meter, and on gravity determination of geophysical exploration. Also, the author analysed the inconsistency between different absolute gravity control points that used for CGBN-85 (China's gravity basic network-85), the inconsistency between CG BN-85 and china's first order gravity network Finally, on regarding the unification of our country's gravity networks, some usefull suggestions were given.