Abstract: Aiming at the problem that horizontal wells in heavy oil reservoir with bottom water drive of Subei oilfield are prone to produce water cones and are always in a state of low production and low efficiency after the production enters the ultra–high water cut stage, the CO_2 huff and puff is an effective measure to improve the production of low-efficiency heavy oil horizontal wells. Therefore, the horizontal wells in HZ block are selected to carry out CO_2 huff and puff test, and the reasonable parameters and matching technology of CO_2 huff and puff are studied, and the factors affecting the effect of CO_2 huff and puff are analyzed. The results show that the main factors affecting the effect of multi-cycle CO_2 huff and puff in horizontal wells include the selection of horizontal wells, CO_2 injection volume, gas injection intensity, injection speed, injection pressure, well closure time and oil production intensity, etc. Adding CO_2 corrosion inhibitor, injecting CO_2 into fixed string and using pumps to produce oil are the matching technology.