The invention discloses a method for preparing liquefied natural gas by converting raw materials of coke oven gas and blast furnace gas. In the technology, the coke oven gas and the blast furnace gas are taken as the raw materials, the raw materials are subjected to normal-temperature normal-pressure dry desulfurization, gas compression, gas adsorption purification, gas isothermal-adiabatic serial methanation, gas adsorption drying and demetalization, freezing liquefication separation and other technical processes, and high-quality liquefied natural gas with the purity of over 99 percent is produced. By the technology, harmful impurities such as sulfur, naphthalene, tar, benzene, mercury and the like in the gas can be efficiently and easily removed fully at low cost, and components with low value, such as H2, CO, CO2 and the like are completely converted into required CH4 component with high value, so the method has the characteristics of low requirement on quality of feed gas, high yield of liquefied natural gas product, high product purity, low production energy consumption, no environmental pollution, reliable flow, low investment, simple operation and good economic benefit.