The invention provides a pool testing method of low-frequency acoustic directivity of a large submerged buoy vector hydrophone. The pool testing method comprises the steps of (1) placing a submerged buoy system to the center of a pool, placing a low-frequency/very-low-frequency acoustic source to a position which enables the vector hydrophone in the submerged buoy system to be positioned in an acoustic source near field and the center of the vector hydrophone and the acoustic source to be positioned at the same placing depth, wherein the sound filed at the position of the vector hydrophone expands in a spherical wave mode; (2) determining the range of a rotary angle of the submerged buoy system according to the dimension of the submerged buoy system and equivalent conditions of testing results of the spherical wave and testing results of a plane wave; and (3) enabling the whole submerged buoy system to rotate at a low speed, recording signals when emission frequency of a sound pressure channel of the vector hydrophone is f0 in real time, and performing post-processing to obtain low-frequency/very-low-frequency acoustic directivity of the submerged buoy vector hydrophone. By means of the pool testing method, the testing of the acoustic directivity of the complicated vector hydrophone system can be achieved in a high precision mode in the pool which can be controlled easily, and accordingly, the requirements of further research are met.