Global ocean tides data were derived from Geosat altimeter data by means of the Quasi-Harmonic Constituent Method (QHCM). Tidal solutions with resolution of 1°/3 in longitude and latitude were obtained for constituents M2, S2, O1, K1, M4 and MS4. The mean sea heights above the reference ellipsoid were also obtained consequently. The obtained tidal constants were compared with those from deep-sea and island tide gauge data. The rms differences between the harmonic constants derived from Geosat altimetry and deep-sea tide gauges for M2, S2, O1 and K1 ranged from 1.4 cm to 2.6 cm, although the GM altimeter data have significant errors due to instrument malfunction and other reasons. M2 tide obtained was the most accurate one among all the tides. Comparison also showed that island tidal constants cannot represent well the tidal distribution in the ocean near the island, because of the significant local effect on tides.