Oilfield are rich in remaining oil, positioning CO2 flooding as a promising enhanced oil recovery (EOR) technique. However, the inherent reservoir heterogeneity, coupled with the differing mobilities of oil and gas, poses a substantial risk of gas channeling during CO2 injection. Water-alternating-gas (WAG) injection, a widely recognized method for mitigating gas channeling, requires further investigation to assess its effectiveness in this region. This study employs natural conglomerate cores with varying permeabilities to evaluate the impact of WAG on the performance and oil recovery of CO2 flooding under heterogeneous conditions. The results indicate that WAG significantly reduces intra-layer gas channeling, but the aqueous phase dampens the interaction between CO2 and crude oil, leading to a reduction in low-carbon components in the produced oil. Furthermore, when inter-layer and intra-layer heterogeneities coexist, the effectiveness of WAG in controlling channeling and enhancing oil recovery diminishes, highlighting the need for additional mobility control techniques, such as in-situ foam. This research offers valuable insights into the feasibility of WAG in the Bai 21 well block and provides practical guidance for optimizing gas channeling control strategies in similar heterogeneous reservoirs.