The invention discloses a burner with a gasification agent and a raw coal gas which are mixed completely and a complete mixing and gasification method for the gasification agent and the raw coal gas,relates to the burner and a gasification method applying the burner, and aims to solve the problems that slag is bonded at an ejection hole of a conventional burner and slag is blocked at a slag discharge hole. The burner comprises an annular external gasification agent channel, an external gasification agent nozzle, an annular gas channel, a central gasification agent channel, a gasification agent main tube, a central gasification agent flow adjusting valve, an external gasification agent flow adjusting valve, a central gasification agent conveying pipeline and an external gasification agentconveying pipeline. The method comprises the following steps: I, aligning the burner to a gasification chamber, and ejecting a raw coal gas into the gasification chamber from the annular coal gas channel; II, dividing the gasification agent into two air flows by the gasification agent main tube; III, ejecting the two flows of the gasification agent into the gasification chamber from the external gasification agent nozzle and the central gasification agent channel. The burner is applied to the field of raw coal gas purification.