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In order to study the role of P in super ferritic stainless steel, based on the composition of S44660 steel, the mass fraction of P was adjusted, and the P content was controlled to 0.004%, 0.009%, 0.033% and 0.055%, respectively, and the effect of P content change on the microstructure and mechanical properties of cast S44660 super ferritic stainless steel was studied. The results show that: P can expand the crystallization temperature range (ΔT), reduce the grain size and increase the equiaxed crystal rate when the P content is 0.009% and 0.033%, but when the P content is 0.055%, the grain size increases and the equiaxed crystal rate decreases; The right amount of P can improve the room temperature tensile properties and hardness of the material; P has a dual effect on the impact toughness of the material, on the one hand, P has a refinement effect on the grain, thereby improving the impact absorption work of the material, on the other hand, excess P will promote its deflection at grain boundaries, which in turn affects the toughness of the material.