This study was conducted to determine the sound paths and transmitted sound level in house. An air-conditioner system was selected a typical sound source. The measured transmission loss data shows that the apertures have an significant effect on the transmitted noise and comparable with the existing theoretical data. Therefore the complex aperture was substitute to quantitative apertures approximately. An effective simulation method, ray tracing and mirror image source method, was employed in the prediction of transmitted sound level. The measured results were efficiently reflected on the simulated results. So it is important that measuring the acoustic parameter prior to the prediction of the transmitted sound level in the house.