A logging-while-drilling(LWD） quadrupole composite transmitting transducer based on metal substrate structure is designed in this paper. The frequency domain and time domain acoustic responses of transducer are numerically simulated by the finite element method. The effects of the collar structure and excitation pulse width on its acoustic characteristics are investigated. A practical transmitting transducer is fabricated and encapsulated for the experimental test in the anechoic water tank. The test results show that the resonant frequency, emission voltage level and horizontal directivity of the transmitting transducer are in good agreement with the numerical simulation results. The transducer has a first-order bending vibration mode near the frequency of 4.7 kHz, and its emission voltage level can reach 126.2 dB. Therefore, it has the characteristics of low frequency and high power radiation, and can meet the requirements of the quadrupole acoustic logging-while-drilling.