Aiming at the problem of low oil recovery in shale reservoir with primary depletion development after fracturing，an experimental method of supercritical CO₂/H2O mixture huff and huff to enhance shale oil recovery was proposed based on the low porosity and ultra-low permeability of shale reservoir. In this paper，the effect of supercritical CO₂/H2O mixture on huffing and puffing shale oil was evaluated by indoor self-designed core experiment，during which the influence of injection medium，soaking time，injection pressure and huff and puff cycles on enhanced oil recovery（EOR）was studied. At the same time，the producing ratio of oil in different pores by supercritical CO₂/H2O mixture was determined by nuclear magnetic resonance technology. The results show that the supercritical CO₂ /H2O mixture huff and huff can effectively enhance shale oil recovery. The soaking time has a great influence on EOR in shale cores with poor porosity and permeability. The injection pressure is closely related to the diffusion rates and flow capacity of the supercritical CO₂/H2O mixture，and the increment of enhancing oil recovery under miscible conditions is significant. The producing ratio of oil in large pores enhances as the the huff and huff cycle increases，but it is not possible to produce more oil in small pores by increasing huff and puff cycles.