Abstract: As for oil reservoirs after polymer flooding,the reservoir has the characteristics of fast rising water cut,large production decline rate and great difficulties in the residual oil production.The endogenous microbial oil displacement field test of small block has been carried out in the east of Nan-2 block of Daqing oilfield.The research on injection pattern,injection process and reservoir dynamic change has been analyzed.The results indicate the injection mode of jointed protection slug can fully activate the effect of nutrient and it is helpful for microbial oil displacement effect.Endogenous microbial flooding increases the light components of crude oil,thus it improves the liquidity of crude oil.The producing condition of reservoir profile and the production volume of poor reservoirs can be improved.The highest increased oil production of the tested 4 wells is 13.4 t/d and the composite water cut can be decreased by 2.2%.All these indicate that the oil reservoirs after polymer flooding can also adopt the endogenous microbial flooding to further increase oil recovery.