The invention relates to a method for manufacturing melt-through resistance high alloy casting steel of an internal-casting cooling water pipe, which comprises the following steps: the internal-casting cooling water pipe is put in a casting mold, and high-alloy molten steel is casted; low-pressure nitrogen is firstly blown into a steel pipe before the casting begins, and bottled industrial nitrogen with the pressure of 0.8-1.2MPa is continuously blown in during the casting process; the bottled industrial nitrogen is continuously blown in after the casting is finished; and the casting mold is originally placed for 8-16 hours after casting, and then, the demoulding and the heat insulation of a casting are carried out. The invention can be widely applied to the production of heat-resisting iron and copper castings with high thermal conductivity and can greatly reduce the rejection rate of the high alloy casting steel of the internal-casting cooling water pipe.