The invention provides an application of in-situ combustion flue gas to oil deposit exploitation and a system. According to oil deposit exploitation, the flue gas generated by in-situ combustion is reinjected into an adjacent oil reservoir of the in-situ combustion to achieve gas driving of the oil reservoir. Equipment at least comprises a fireflooding oil reservoir and a steam injection oil reservoir. The flue gas down-hole reinjection system comprises a casing pipe (21), a gas injection perforating pipe (22) and an oil-extraction oil pipe (23), wherein the gas injection perforating pipe (22) and the oil-extraction oil pipe (23) are arranged in the casing pipe side by side. A one-way valve (29) is arranged at the position, opposite to the bottom of the in-situ combustion, of the gas injection perforating pipe, and a hole (210) is formed in the position, opposite to the steam injection oil reservoir, of the gas injection perforating pipe. A gas-liquid separator (28) is arranged at the position, opposite to the bottom of the in-situ combustion, of the oil-extraction oil pipe. According to the application and the system, effective utilization of the flue gas is ensured, and the ground treatment and reinjection process is simplified; a flue gas injection target oil reservoir is effectively controlled, and therefore the production safety in the air injection process is ensured; due to oil reservoir flue gas driving, the recovery ratio of a heavy oil reservoir is increased, and the emission of greenhouse gas and poisonous gas is reduced.