The invention provides a method for preparing methyl alcohol and dimethyl ether by carrying out sulfur-tolerant isothermal transformation on tail gas of a calcium carbide furnace. The method mainly comprises the following steps: pressurizing, carrying out sulfur-tolerant isothermal transformation, carrying out temperature swing adsorption purification, carrying out pressure swing adsorption purification, compressing, synthesizing methyl alcohol and dimethyl ether, synthesizing purge gas and extracting hydrogen, and carrying out waste gas treatment. A transformed technology enables operational flexibility of a production system to be higher, balance production can be carried out with or without sodium chlorate tail gas, all the tail gas of the calcium carbide furnace can be utilized, yield is increased, and a sky lantern is not lighted, so that the environment is not polluted. By reducing wet desulphurization, dry desulphurization, deoxidization and dearsenization processes, energy loss in a gas transportation process is reduced. Besides, pressure swing adsorption hydrogen recovery rate is increased, and the aim of saving energy is achieved. The improved technology is advanced, technological process is greatly shortened, whole program control on operation is realized, and a man-made operational error is reduced.