An inexpensive sheet material of a copper alloy has excellent bending workability and excellent stress corrosion cracking resistance while maintaining high strength. The sheet material is produced by a method including melting and casting raw materials of a copper alloy which has a chemical composition having 17 to 32 wt. % of zinc, 0.1 to 4.5 wt. % of tin, 0.01 to 2.0 wt. % of silicon, 0.01 to 5.0 wt. % of nickel, and the balance being copper and unavoidable impurities; hot-rolling the cast copper alloy at 900° C. to 400° C.; cooling the hot-rolled copper alloy at 1 to 15° C./min. from 400° C. to 300° C.; cold-rolling the cooled copper alloy; recrystallization-annealing the cold-rolled copper alloy at 300 to 800° C.; and then, ageing-annealing the recrystallization-annealed copper alloy at 300 to 600° C.