Abstract: The model analyzing production decline and deciding the main factors is helpful to the development of oilfield.The reservoir production rate is composed of such parts as the production rates of measured wells，old wells and new wells.And the production decline rate is the production rate weighting sum of every part decline rate.The main part which affects the production decline rate is decided according to the contribution values of every part.Then the production decline rate of every part is grouped into four factors as liquid rate，oil cut，well-opening numbers and producing time,which can be easily controlled in the field.The diagnose model between production decline rate and the four factors is set up.According to the model the main factors which have great effect on the production decline rate can be easily decided.This research can provide criteria to take steps to slow down the production decline rate.

Key words: water flooding reservoir, production decline rate, diagnose model, production construction, affecting factors