Abstract: Acoustic look-ahead detection while drilling is a key technology for geosteering, enabling the advanced identification of formation interfaces ahead of the drill bit, which is of great significance for the safe and efficient exploration of complex oil and gas reservoirs. However, existing logging-while-drilling (LWD) technologies are primarily based on seismic and resistivity methods, while the development of dedicated instruments for acoustic look-ahead detection is still in its infancy, and breakthroughs in the theoretical foundations of wavefield propagation and signal extraction are urgently needed. To this end, a 3D finite-difference time-domain method is employed to construct a numerical model containing a single formation interface. The effects of acoustic array configuration, look-ahead interface distance, source excitation modes, and dominant frequency on the signal-to-noise ratio (SNR) of reflected waves and wavefield characteristics are systematically investigated. Combined with time–slowness correlation analysis, the formation mechanisms of the complex acoustic field are revealed. The results indicate that the "upper transmitter, lower receiver" array configuration yields higher SNR at short source–receiver spacings. Compared to monopole sources, dipole sources with a dominant frequency of 2–3 kHz improve the SNR of reflected waves by nearly 20 times, and the wavefield is dominated by shear waves, making it more favorable for look-ahead interface signal processing. This study provides a reference for acoustic array layout optimization, source parameter optimization, and reflected wave identification in acoustic look-ahead detection while drilling instruments.