The present invention discloses a heat recovering type fuel gas preparation system. The system comprises: an entrained-flow gasifier, a waste heat boiler connected with the top of the entrained-flow gasifier, and a lock hopper connected with the bottom of the entrained-flow gasifier. The entrained-flow gasifier is provided with at least two secondary oxygen supplying nozzle chambers, wherein the secondary oxygen supplying nozzle chambers are respectively provided with a secondary oxygen supplying nozzle, respectively positioned below a process nozzle chamber provided with a process nozzle, and are symmetrically arranged on the circumference of the main body of the entrained-flow gasifier. The invention further discloses a fuel gas preparation method by adopting the fuel gas preparation system. The method comprises that: an oxidizing agent is introduced to the secondary oxygen supplying nozzle chambers during the gasification reaction process to promote the further gasification reaction; the resulting fuel gas generated from the reaction enters the waste heat boiler to carry out heat recovering; the generated liquid residue is discharged downward by the lock hopper. The system and the method of the present invention have characteristics of strong adaptability of the raw materials, good indicator, flexible operation, sanitation and environmental protection.