Loudness is one of the most important parameters of psychoacoustics. In the past, most loudness models were applicable only to steady sounds. However, most everyday sounds are time-varying. Moore and coworkers described a time-varying loudness model based on Moore’s Loudness model. In this paper, a detailed calculation of Moore’s time-varying loudness model is given. The model using the time waveform of a sound which is picked up by the microphone as its input is implemented in Visual C++. The results which are compared with LabVIEW and ANSI show that the system is feasible.