A method for endoscopic ultrasonic phased array imaging was proposed based on high-precision digital beamforming. Based on conventional digital beamforming, a new digital beamformer with A/D converter of high sampling rate was designed. Compared with the conventional digital beamformer, the delay precision of the new digital beamformer is upgraded to 1.4 ns from 8 ns. In this paper, we used the new digital beamformer to synthesize the ultrasonic signals received by the array elements. Then we utilized the digital quadrature demodulation circuit to realize envelope extraction of the synthetic ultrasonic signal. Finally, using iron wires in water tank as experimental sample, the experiment results show that using the digital beamforming technology, the peak sidelobe is effectively suppressed, and the lateral resolution and SNR are improved by 25% and 3.7 dB respectively.