The invention discloses plastic mold steel and a mold for forming plastics. The plastic mold steel comprises the following chemical components by weight percent: 0.38 percent of C, 0.9 percent of Si, 0.5 percent of Mn, 13.6 percent of Cr, 0.3 percent of V, less than or equal to 0.003 percent of S, less than or equal to 0.02 percent of P, and the balance of Fe. The plastic mold steel has good corrosion resistance, after the mold for forming the plastics and manufactured by adopting the plastic mold steel is used for a long time, the surface of a mold cavity is still maintained at an original state, parts such as a cooling water pipeline are slightly subjected to the corrosion, the heat conductivity and cooling efficiency are maintained stable, no protection layer is needed, the production cost and maintenance cost of the mold are reduced, and the production cost of the plastic product is reduced.