Abstract: Non-destructive testing methods had attracted wide attention in recent years, and it was found that ultrasonic testing was an effective way for fruit early internal damage detection. However, the sound energy cannot easily penetrate the fruit for effective testing due to its grain characteristic of it, leading to great attenuation of sound. A multi-vibration, low frequency and high emission energy ultrasonic transducer based on PZT-4 thick wafer was thus developed in this paper. The mathematical model of the sensitive element was established, and the performances of the transducer were researched under different excitation conditions and optimized with the help of experimental testing. At last, the practicality of the transducer has been verified by further experiments. The designed transducer with high sound emission energy and small diameter achieved effective coupling with the fruit surface, well penetration to a fruit, such as apple and pear for example, for early inner damage testing.