After waterflooding development for several decades，the majority of old offshore oilfields have entered the stage of high water cut，low production and serious invalid water cycle. Therefore，it is necessary to study the remaining oil distribution and enhancing oil recovery technology for low producing degree. CO2 immiscible flooding is usually implemented after water flooding，so the effect of injected water remained in the pores on gas injection development needs to be taken into account. Based on the traditional method of researching the remaining oil distribution，the combination experimental method of online CT scan of core and micro-model simulation of core was proposed to qualitatively and quantitatively analyze the characteristics of water flooding，gas drive and remaining oil distribution from core scale and micro pore scale at different times. The start-up mode and migration process of the remaining oil after water，gas and WAG injection were revealed. The mechanism of water injection and gas-oil displacement and macroscopic and microscopic distribution characteristics of remaining oil after oil displacement were researched quantitatively and qualitatively from the aspects of macroscopic core scale and microscopic pore structure. The start-up mode and migration process of the remaining oil during gas drive after water flooding and water alternating gas flooding were revealed. The three-phase flow rules of oil，gas and water under the action of movable water have been further described，which provides theoretical basis and experimental basis for the development of CO2 immiscible flooding.