The invention relates to a method for fixing a reinforcing fiber during molding of a resin material workpiece. The method comprises the following steps that an obtaining step is performed, wherein a viscosity temperature curve of a resin material for producing the workpiece is obtained; a determining step is performed, wherein the temperature range of a low-viscosity platform of the resin materialis determined according to the viscosity temperature curve; and a fixing step is performed, wherein the resin material in the temperature range is jetted on the reinforcing fiber so as to fix the reinforcing fiber to a mold for molding the resin material workpiece. The invention further relates to an jet device for fixing the reinforcing fiber in the method. The jet device comprises a container for containing the resin material, a nozzle, a compressed air source, a gas pipeline connecting the nozzle with the compressed air source and a fluid pipeline connecting the nozzle with the container,and further comprises a heating device, a temperature measuring device and a heating control system, the heating control system is connected with the heating device and the temperature measuring device and can control the heating device so as to control the resin material in the container to be in the low-viscosity platform.