Based on its geological characteristics and development needs, Liaohe Oilfield has successfully implemented CO2-assisted steam huff-n-puff technology, and significantly improved the recovery degree. It not only enhances the sweeping efficiency of steam and maintains reservoir pressure with the aid of CO2, but also plays a role in assisting drainage and reducing oil viscosity. However, during the application process, due to the injection of two agents, the traditional injection method is hard to achieve a fine control over multiple sets of strata. This work introduces a layered quantitative fine injection technique achieved via a composite injection packer and a composite layered injection device. It has been verified to significantly improve the vertical sweeping efficiency by 20–30%. As of January 2024, such novel devices and technique has been applied in 32 wells with 100% success rate. Cumulative increased oil production has reached 11,000 tons. Pilot tests have verified that such technique can accurately control the injection volume of each layer, and the special-designed packer can stably run under the condition of alternately injecting CO2 and high-temperature steam, and further simplify the surface injection process. This work provides an effective technical support for the heavy oil thermal recovery with a wide-spread application prospects and a leading role in technical demonstration.