The invention relates to a machining process and device for filling a weak-rigidity spare part with paraffin. The method comprises the following steps of: melting paraffin, hierarchically casting the paraffin, and the like, wherein the paraffin is melted in a paraffin casting device by a water bath heating device close to the bottom of the paraffin casting device; and melt paraffin is hierarchically cast through the control of a ball valve. The invention can improve the processing rigidity of the weak-rigidity spare part, improves the processing effect and has the advantages of convenience for operation, simple structure and capability of recycling.