The invention discloses steel for 3.5 Ni and a production method thereof, and relates to the technical field of steel production, and the steel comprises the following chemical components in percentage by mass: 0.030%-0.080% of C, 0.10%-0.30% of Si, 0.50%-0.90% of Mn, less than or equal to 0.005% of P, less than or equal to 0.002% of S, less than or equal to 0.0050% of residual Nb, less than or equal to 0.003% of residual V, less than or equal to 0.005% of residual Ti, 3.30%-3.70% of Ni, 0.05%-0.20% of Cr, 0.05%-0.20% of Mo, less than or equal to 0.050% of Cu, 0.020%-0.050% of Al, 0.0008%-0.0020% of Mg, less than or equal to 0.0060% of N, less than or equal to Through a series of process improvements of smelting, rolling, heat treatment and the like, the process problem of intergranular cracks of the steel grade is solved, the advantage of batch smelting and manufacturing of the steel grade is obtained, the manufacturing stability is greatly improved, and the manufacturing cost is greatly reduced.