The synthetic aperture (SA) beam forming can realize bidirectional dynamic focusing in both transmission and receiving, so it improves the imaging resolution effectively and will be widely used in the multi-element phased array ultrasonic endoscope system. However, because of the low transmission energy of the single element, the echo signals are weak and could be influenced by noise easily, thus the signal-noise ratio (SNR) of the image is relatively poor. A new imaging algorithm is proposed, which combines the Barker coded excitation using the linear frequency modulated carrier with the synthetic aperture beam forming (LFM Barker SA). The broadband of linear frequency modulated signal and the autocorrelation of Barker can remedy the SNR of synthetic aperture beam forming, and the proposed algorithm improves the imaging resolution further. The simulation results with FieldⅡ software show that the LFM Barker SA algorithm improves the SNR about 10 dB and increases the axial resolution from 0.60 mm to 0.38 mm, compared with the Pulse SA algorithm. The experimental result verifies the feasibility of this algorithm.