The invention relates to a F6NM martensitic stainless steel cylinder-body forge piece and a heat treatment method. According to the F6NM martensitic stainless steel cylinder-body forge piece and the heat treatment method, the high strength and the high low temperature impact toughness resistance can be met, cracks are avoided, and meanwhile, cracking and scrap of steel ingots during forging are avoided; and the F6NM martensitic stainless steel cylinder-body forge piece comprises, by mass, no more than 0. 04% of C, 0.30-0.50% of Si, 0.70-1.00% of Mn, 11.5-13.0% of Cr, 3.5-4.5% of Ni, 0.50-0.70%of Mo, 0.04-0.1% of V, no more than 0.020% of P and no more than 0.010% of S. The F6NM martensitic stainless steel cylinder-body forge piece has the advantages that the F6NM martensitic stainless steel cylinder-body forge piece after being subjected to component optimization adopts sectional-type constant-temperature slow heating, the charging temperature, the heating speed and the heat preservation time are strictly controlled, forging is strictly executed according to the new forging process, and heat treatment adopts the special heat treatment process of 550 DEG C constant-temperature heating, 1000 DEG C air quenching and three times of tempering at 690 DEG C, 630 DEG C and 590 DEG C. After production, product inspection dimensions confirm to the customer drawing requirements, a sampleis sampled and sent to a third party for being tested, the mechanical properties meet the index requirements, after multiple times of production, the mechanical properties of the F6NM martensitic stainless steel cylinder-body forge piece are all very stable, and the F6NM martensitic stainless steel production scrap risk is greatly reduced.