Abstract: Adjoint method was used to deduce M₂ tidal harmonic constants on the open boundary of the Bohai Sea by using M₂ tidal harmonic constants in the inter iorregion.To improve the results of numerical simulation,the prescribed bottom friction coefficients were also adjusted by adjoint assimilation.Four experiments were car ried out.Experiment 1 uses only har monic constats at 19 tidal stations;Experiment 2 uses harmonic constants at 37 points on the T/P Satellite Tracks;Experiment 3 uses all the above data;Experiment 4 uses har monic constants at 19 tidal stations and 14 selected points on the T/P Satellite Tracks.The averaged absolute differences between the simulated and the observed are as follows respectively.For Experiment 1 the averaged absolute difference of the amplitude is 2.4 cm and the averaged absolute difference of the phaselag is 5.0°.For Experiment 2 they are 4.4 cm and 5.7°respectively.Experiment 3 gives 5.5 cm and 8.5°respectively.And Experiment 4 gives 3.3 cm and 5.6°respectively.The results of the four experiments coincide with the observed M₂ tide in the Bohai Sea fairly well.