The invention relates to a method decreasing steam temperature in steam pipe. After cooling water and steam, which are delivered into steam pipe in the same time, are mixed and atomized, they are sprayed into steam pipe; the pressure of steam delivered into steam pipe is at least 0.05Mpa more than the pressure of cooling water and the weight of steam is 1-5% of cooling water; the mixture of steam and cooling water is sprayed into steam pipe from the middle of steam pipe. Steam is delivered to the nozzle set in steam pipe by separate pipe; the pressure of steam after depressurization is less than the pressure of cooling water in nozzle hole so that cooling water is absorbed to nozzle hole and mixed with steam from separate pipe delivering cooling water, which is connected to nozzle; mixture of steam and cooling water after mixing is sprayed in steam pipe. By the invention, cooling water is sprayed fully and the atomization performance is good; it can provide steam with suitable temperature, which comes up to the usage condition, to department using steam and energy is saved.