Abstract: Aiming at the problem that the directivity of large low frequency transducer is difficult to measure, a measurement method based on four-element cross array is proposed in this paper. By measuring the time delay differences between the four-elements of the cross array and combining with the hyperboloid intersection method to locate the transducer, the measurement of the directivity of large low frequency transducer can be realized by measuring the acoustic signals received by the four-elements of the cross array. The transducer locating algorithm is simulated according to the measurement method, and the corresponding lake experiment is designed for measuring the directivity of the simulated sound source based on this method. The measurement results are analyzed and compared with the results of the laboratory measurement method in anechoic tank. It is shown that the difference between both measurement results of -3dB beam width is within 10%, and so this method can be used for testing the directivity of large low frequency transducer in modern sonar equipment.