We propose a rectangular transverse through-hole wideband tonpilz transducer using multimode coupling. To excite a vibration mode that can be coupled with the longitudinal vibration for broadening the frequency band, a rectangular through-hole is opened at a certain distance from the front head of the conventional longitudinal vibration tonpilz transducer. To achieve the best bandwidth, the finite element method was used to optimize the length and width of the through-hole and the distance between the front end of the hole and the end surface of the front head. In addition, to obtain the best hole position and size, a prototype tonpilz transducer was developed. The test results show that the transducer has three main operating modes within 12-32.5 kHz, and the latter two modes contribute to the widening of operating bandwidth. A longitudinal vibration tonpilz transducer of the same size with no hole has a 3 dB bandwidth of only 3 kHz, whereas the holed transducer has a bandwidth of 10.5 kHz. Effectively expanding the working bandwidth shows that the theoretical calculations and experimental results are in good agreement.