Abstract: To address the development challenges of production decline and water cut rise in the later stage of steam huff and puff in the extra-heavy oil reservoir of Mortuk Oilfield, this article verifies the feasibility on field of multi-component thermal fluid (MCTF) huff and puff technology and optimizes the parameters for injection-production. The synergistic oil-increasing mechanism of MCTF was revealed through displacement simulation tests, and key parameters such as steam injection rate and gas-steam ratio were optimized using CMG (computer modeling group) numerical simulation software, and field application tests and comparison with the effects of steam huff and puff were conducted. The results show that the optimal thermal recovery parameters for the oilfield are as follows: steam injection rate 150 t/d, gas-steam ratio 300 m³/t, CO₂ proportion 70%, injection time 20 d, and soaking time 5 d. A total of 61 well-times of field implementation were carried out, with a measure efficiency of 96.7%, an average single-well daily oil increase of 3.8 t, and a cumulative oil increase of 29 989 t. Also the steam injection time, soaking time and water drainage time were significantly shortened than steam huff and puff, and the oil increase effect of horizontal wells was better than that of vertical wells. The outcome of the study can effectively improve the development effect of extra-heavy oil reservoirs in the later stage of steam huff and puff, providing technical reference for similar reservoirs development.