Abstract: Due to having low C content，medium Ni content and fine lath ageing martensite with proper post-heat treatment toughness，the 17-4PH martensite precipitation-hardened stainless steel should have presented fine hot-cutting ability and weldibility in the hot-working state. However during the actual hot-working process，this steel is prone to develop crack defects when being subjected to hi-energy rate hot-cutting and welding. Thanks to analyzing the principle of occurrence of cracks with the said 17-4PH stainless steel during the plasma hot-cutting process and the welding operation，the hot-process of the work piece is traced and analyzed，and then causes for occurrence of cracks with the said stainless steel during the above mentioned hot-cutting and welding processes are identified. Accordingly relevant measures have been taken to get the said cracks avoided.