The invention relates to alloy steel for a high-strength gas cylinder. The alloy steel consists of the following chemical components in percentage by weight: 0.30-0.38 percent of C, 0.15-0.37 percent of Si, 0.60-0.90 percent of Mn, 0.80-1.20 percent of Cr, 0.15-0.30 percent of Mo, 0.01-0.05 percent of Al, 0.00-0.25 percent of Ti, 0.02-0.25 percent of Nb, 0.03-0.20 percent of W, less than or equal to 0.010 percent of P, less than or equal to 0.010 percent of S, 0.002-0.004 percent of Ca, less than or equal to 0.0035 percent of N and the balance of Fe and inevitable impurities, wherein Ti+Nb is more than or equal to 0.07 percent; and the total quantity of impurity elements is less than 0.05 percent. A manufacturing method of the high-strength gas cylinder comprises the following steps of: smelting, refining, performing VD (Vacuum Distillation) treatment, controlling the content of elements P and S in the steel, and adjusting the content of N simultaneously; before tapping, feeding Si-Ca wires in an amount of 2-3 meters into every ton of steel for denaturalizing inclusions; pouring a square billet with a large square billet continuous casting machine under the protection of argon gas, blooming at the temperature 1,050-1,090 DEG C, and cogging to obtain a square billet material; manufacturing a seamless gas cylinder; preserving the heat of the seamless gas cylinder at the temperature 800-940 DEG C for 30-60 minutes, and performing water quenching treatment; and tempering at the temperature 500-650 DEG C, and preserving heat for 30-120 minutes. The obtained gas cylinder steel has a tempered sorbite structure, the tensile strength is over 1,100 MPa, and the low-temperature impact toughness at the temperature 50 DEG C below zero is over 45 J/cm<2>.