Abstract: In order to solve the problem that it is difficult to determine the sampling range in the flame cutting sampling process of 50Mn steel plates with different thickness, the range of the heat affected zone of 5 mm thickness 50Mn steel plates under oxygen-acetylene flame cutting conditions was studied by experiment and numerical simulation, and the simulation accuracy was verified by hardness test. The temperature field of 50Mn steel plates with different thickness during flame cutting process was simulated by using the software FLUNT, and the range of the heat affected zone in flame cutting of 50Mn steel plates with different thickness was obtained. The width of the heat affected zone and the thickness of the steel plates were linearly fitted, and the relationship between the minimum machining allowance Y and the thickness of 50Mn steel plates x was Y=1+int(10.31+0.11x).