Abstract: In order to determine the natural production decline of horizontal wells in bottom water reservoirs,by considering geological and dynamic factors, the mechanism model of heavy oil bottom water reservoirs in western Q oilfield was established, and the theoretical chart between the influencing factors and the natural production decline rate of horizontal wells were given. The results indicate that in the horizontal well development of bottom water reservoirs, the production decline rate may be reduced to 20% when the water content reaches 80% under the condition of low fluid production speed, and the production decline rate can be maintained at 10%～20% when the controlled reserves of the horizontal well reach 10%. Through comparing the theoretical drawing with the actual horizontal well, the results conform to the actual production, which is of great significance for judging whether the oil well is in normal production and later production prediction.