Abstract: The influence of the tidal effect on the test data, especially the build-up pressure data, is sometimes very obvious. In order to retain the true reservoir pressure variation characteristics, the measured pressure data must be corrected to eliminate the influence of tidal effect. The influence of shut-in time, tidal size and formation permeability on well test curve have been analyzed. The tidal data is indirectly by using the equipment of the offshore platform, or the tidal data of the port near the well site is used, and the welltesting interpretation software is used to correct the measured well testing pressure data to eliminate the influence of the tidal effect as much as possible. The well test interpretation was performed on the corrected pressure data, and a good fitting effect is obtained, which is of great significance for well test interpretation in offshore oil field in the future.