Synthetic aperture focusing, widely used in radar system, is introduced into endoscopic ultrasound imaging system in this paper. Based on the features of synthetic aperture focusing (SAF), a method of synthetic aperture imaging for ultrasonic endoscope is presented, using the rotation effect of a probe with single transducer, transmitting and receiving the echoes at different time and different locations during the rotation, synthesizing a large transmitting aperture equivalently to enhance the signal to noise ratio and the resolution of the ultrasonic images. The principle of synthetic aperture technique was analyzed, which is used for endoscopic ultrasound imaging with single transducer probe, and then the longitudinal and lateral compression were implemented according to the coded and linear frequency modulated characteristics of the echoes. Finally, an experiment was completed, using a transducer, with the center frequency of 8 MHz, to detect a pigskin sample, the target with the size of 0.8 mm×2 mm could be identified, and the signal to noise ratio had an improvement of 9.38 dB.