Abstract: The accuracy of frogman Ultra-Short Base Line (USBL) positioning in shallow water largely depends on the direction finding accuracy of the array, which is determined by time delay estimation accuracy. Due to the robust environmental adaptability of adaptive time delay estimation method, the mixed modulated Lagrange explicit time delay estimation (MMLETDE) algorithm is applied to direction finding in frogman USBL positioning, which could modulate the decimal delay filter to the center frequency of beacon signal and provide higher time delay estimation accuracy with lower orders, when the center frequency of beacon signal is known. According to the USBL array geometry and the features of the array signals, the use of MMLETDE under low signal to noise ratio (SNR) is discussed and simulated, and the results show that the direction finding accuracy of 1 °~3 ° could be obtained under medium or low SNR.