The sound intensity measurement of giant mechanical and electrical equipment is a difficulty when it is tested in the typical condition. Therefore, the sound intensity measurement is employed in the research of sound power level measurement of giant mechanical and electrical equipment in the producing condition. Discrete point method and scanning method, the two ways of sound intensity measurement, and the basic theory of separation of sub-surface test have been studied through theoretical analysis and practical testing. When the two ways of sound intensity measurement are used in overall test, they are compared with the way of dividing the surface into several sub-surfaces. The results show that the two ways of sound intensity measurement for giant mechanical and electrical equipment both can meet the requirements of the engineering test precision and the same test results can be achieved when using sub-surface test. Besides, the sequence of the sound power levels of the complex multi-source equipment can be carried out by using sound intensity test of sub-surface so as to identify the main noise sources of the equipment.