Earlier experimental study on late water flooding are mainly focused on water flooding timing and seldom on injection-production pattern. There was error for gas and liquid separation and human reading on the outlet by traditional methods of oil displacement efficiency. An oil field abroad was taken as the research object. The influence of water flooding timing and injection-production pattern on late water flooding effect was researched on conventional oil phase behavior and oil displacement efficiency during late water flooding. Based on the study of conventional phase behavior，the influence of water injection pressurization on the phase behavior was evaluated. In the experiment method of oil displacement efficiency，the on-line NMR technique was used to evaluate the oil saturation of core in the displacement process in real time and then the accuracy of the result was improved. The results show that the water flooding recovery reached to 16.5% when water flooding was performed at 34% of saturation pressure during the depletion development. Considering the production rate，development costs and other factors，water injection was superior when the bubble point pressure was around 80%. For the long-term depletion development of severe degassing blocks，the development way of water injection pressurization can be taken. The water flooding effect was the best when the bubble point pressure increased to around 80% by water injection pressurization.