Abstract In the precise calculation of tidal generating force,the effect of earth flattening is a part that must be taken into account. We have computed the magnitude of the effect of earth flattening to the tidal generating force of the moon and the sun, and analyzed the space characters and frequency characters of the effect. In addition, we have carried out harmonic development of the effect of earth flattening on generating tidal potential of the moon by use of the ELP200085 moon ephemeris. The results show that the effect of earth flattening on the tidal generating force is close to 2×10 -11 ms -2, and there are 16 waves with the amplitude bigger than 4×10 -13ms-2 in the developed results.
