Regarding the issue of tide level control in the bathymetry of the long Panjin Channel，this paper studies the tidal theory and builds a tide level calculation model by a tide level calculation technology based on tidal harmonic analysis according to the specific situation of the Panjin Channel to control the tide level of the long distance offshore channel. By comparing the measured data on the tide level at fixed points at sea with the calculated tide level data and the measured data on the underwater topography along the channel in different time periods，the paper finds that the data obtained by the two methods all meet the requirements of the relevant specifications. The results fully testify to the point that the tide level calculation technology based on tidal harmonic analysis is accurate and reliable，can meet the accuracy needs of bathymetry，and can thus be used in the bathymetry of long channels of the same type.