The deep heavy oil reservoir in Ji 7 area is developed by water flooding，and the emulsion phenomenon is common during development process. In order to understand the effect of emulsification on the development，the emulsification characteristics of the produced fluid were analyzed，the wetting types of produced fluid was determined through by the filter paper method，and emulsifying time was judged by analysis of the change of chloride ion content in water，the emulsion droplet size distribution was observed under a microscope lens and its stability was evaluated. Experimental results showed that the crude oil in JI 7 had special emulsification property. That is，the oil and water could be emulsified spontaneously and quickly even if without the addition of emulsifiers. The emulsifying time was early，the water content of emulsion was high，and the droplet dispersion was uniform and the size was close to that of microemulsion，exhibiting good stability. The viscosity of the emulsion was 2.23 times higher than crude oil before emulsification，which was favorable for forming stable water drive front，and greatly improving water drive recovery. The recovery rate was predicted to be 15% ，however，the current recovery degree was nearly 20% and the comprehensive water cut was kept at 40%. It was obvious that self-emulsification made the actual development effect far better than predicted.