A three dimension directivity calculating formula for circular piston transducer array is deduced theoretically according to the acoustic wave superposition principle to reveal how acoustic directional transducer array pattern affects the array directivity. The directivity of a 4×6 array, 5×5-1 array, 3×8 array and 2×12 array, which are all composed of 24 piezoelectric transducer array element, are analyzed by the theoretical formula, and the results show that there are significant differences existing in different arrays. The directivity of the square transducer array in various directions is approximately equal, while the difference of the directivity of the rectangular transducer array in length direction and width direction increases when the ratio of length and width increases.