An indoor sound source localization system is built by conventional physical experiment instruments, such as signal generator, DC regulated power supply, digital oscilloscope, DC motor, quad-microphone line array, digital display angle ruler, loudspeaker, and some self-made devices. The DC motor is used to drive the quad-microphone line array and the digital display angle ruler to rotate coaxially. The sound wave signal received by the quad-microphone line array is amplified and filtered and then sent to an oscilloscope. The sound is judged according to the shape of Lissajou figure on oscilloscope. For the source orientation, the rotation angle of the line array is measured by a digital display angle ruler, and then the position coordinates of the sound source are calculated by usin g trigonometric functions. Experimental results show that this method has high accuracy, small error and low cos t for sound source localization.