The mutual interaction of underwater acoustic transducer array elements is one of the most important factors for its transmission performance. The power output from each array element is characterized by mutual radiation impedance between array elements. Recently numerical simulations are often applied to solve this kind of problem. Generally PZT transducer array is used in experiments but mechanical Q of PZT transducer is high and the range of measuring frequency is limited in narrow band. So many sizes of transducer array models are required to evaluate in different frequencies. Composite material piezo-rubber has unique properties. Its flexibility and broadband resonance character by low mechanical Q allow experiments in various frequencies utilizing one array apparatus.Consequently a flexible method of model experiment using piezo-rubber sheet transducer array is introduced. The total power output versus input phase of 3 x 3 piezo-rubber transducer array provides the effects of interaction between array elements in various frequencies and input amplitudes. Also near field 3-D mapping of real power and imaginal power shows radiation performance of this transducer array visually. A clear power reduction was observed in the case of a -180-deg phase shift pattern.