The invention discloses a method for extracting molybdenum from a waste nickel-molybdenum catalyst. The method comprises the specific steps that organic matter, sulphur, heavy metal arsenic and the like which are attached to the catalyst are removed through oxidation volatilization by means of low temperature roasting, then circulation two-stage ordinary pressure alkali leaching is adopted for achieving separation of nickel from molybdenum aluminum, sodium molybdate crude liquid is obtained and is subjected to heating, evaporation and concentration, cooling crystallization is carried out, andfiltering and separating are carried out to obtain a sodium molybdate product. According to the method, no reagent needs to be added in the roasting process, corrosion to roasting equipment is small,the operation condition is mild, the environmental pollution is small, comprehensive recovering and using of valuable metal in the catalyst are achieved, the sodium molybdate product is obtained, therecovering rate of the valuable metal is high, the product additional value is high, and a certain application value is achieved.