The theoretical calculation methods for the noise source intensity of safety valves of ethylene cracking furnaces are introduced, including the API STD 521, the noise and vibration control engineering manual and the Engineering Noise Control：Theory and Practice. By selecting API STD 521 method for calculation and considering the pipeline distance reduction, free space distance reduction, directivity reduction and A sound level correction in the actual working situation, the simulation calculation analysis and research on noise limits in the working platform area of operators are carried out, so as to meet the requirements on noise limits in the operators’ working area of cracking furnaces.