Abstract: Doppler velocity log (DVL) uses phased-array for sound signal transmitting and receiving. The phased-array mode can largely reduce the volume of transducer and promote the adaptability of installation. According to the characteristic of phased-array, compensation of sound velocity for DVL is unneeded, and so the phased-array DVL is popular in low frequency range. In this paper, the basic beam-forming theory of one dimension linear array is introduced, and the transmitting beam and receiving beam of the phased-array DVL are described. The beam-forming method of the 38 kHz plane phased-array DVL developed by TRDI Company is analyzed. This work lays a foundation for developing a broadband long range phased-array Doppler velocity log.