It is the key for Heidaigou open-pit coal mine to realize sustainable, stable, economical and efficient mining to give full play to the advantages of overcasting blast-dragline overcasting mining technology in the combined mining system. With the principle of consistent advancing speed of combined mining system, the model between the production capacity of combined mining process and raw coal production capacity of Heidaigou open-pit coal mine is established. Based on that, with the goal to ensure the effective throw rate of overcasting blast and give full play to the production capacity of overcasting blast-dragline overcasting mining technology, through in-depth analysis of the restrictive relationship between overcasting blast bench height, height of expansion platform for dragline excavating and raw coal production capacity, then the relational model between the production capacity of the dragline overcasting system, the height of the overcasting blast bench, the height of the dragline expansion platform and the raw coal production capacity was established. It was determined that under the condition that the height of the overcasting blast bench was 45m, and the height of the dragline expansion platform was 13m~16m, the raw coal production capacity of the dragline overcasting operation area in the north of Heidaigou Open-pit Coal Mine could be 24.6199 million t/a~27.9865 million t/a, if the single bucket-truck operation area in the south of 500m developed normally, the entire open-pit mine can achieve a raw coal production capacity of 34 million tons/a.