The method of tidal level calculation,with 11 major tidal constituents obtained from the mid tide data harmonic,is promoted in the field of marine surveying and mapping,surveying for dredging and other areas.However,historical tide data of different periods are collected to analysis without tidal synobservation measurement of all stations,and the tide harmonic constant can not meet the precision requirement of water depth correction.By enhancing the correlation of the harmonic constants of the tidal data at different periods to improve the accuracy of tidal level calculation,we propose two harmonic constants optimization methods,and demonstrate the feasibility of residual sea level calculation from the date in different tidal level period in the cases.