The invention discloses H2S 
corrosion-resistant 80-ksi casing steel for 
shale gas. The casing steel is prepared from, by weight, 0.25%-0.29% of C, 0.20%-0.35% of Si, 0.90%-1.10% of Mn, 0.95%-1.15% of Cr and the balance Fe, residual elements and unavoidable impurities. The invention further discloses a preparation method of the H2S 
corrosion-resistant 80-ksi casing steel for the 
shale gas. The preparation method comprises the steps of 
steelmaking, wherein 
pig iron and waste plain 
carbon steel are adopted as raw materials in the 
steelmaking process, a deoxidizing agent is added in the steel tapping process, static blowing treatment is performed in a VD 
vacuum chamber, and 
argon blowing and sealing 
gasket adding for protection are performed during pouring; 
pipe manufacturing, wherein the temperature of a heating zone ranges from 1210 DEG C to 1270 DEG C, and the temperature of a soaking zone ranges from 1240 DEG C to 1260 DEG C; 
heat treating, wherein the heat treatment technologies of spraying and inner axial flow 
water cooling quenching, 
air cooling tempering and straightening under the temperature are adopted. According to the casing steel, the yield strength is 552-655 MPa, the tensile strength is larger than or equal to 655 MPa, the transverse 10*10-mm V-shaped 
impact energy at 0 DEG C is larger than or equal to 40 J, the elongation is larger than or equal to 19%, and the allowed 
hardness change 
delta HRC is smaller than or equal to 3.0.