In tunnel excavation, according to a geological shooting map for underground support, drilling of holes with limited depth is necessary. Machines with drillstring resonant frequency based input had proved their effectiveness in soil penetration. Finite element analysis (FEA) is commonly used to understand a drillstring dynamic behavior. In this paper, we quantify the system dynamics analytically and the influence of control variables of a sonic drill system. Guided by frequency analysis, it was established that the control system should preserve the resonant mode and the weight on the bit as the primary two control variables. From the temporal responses a tradeoff between the drill-bit amplitude, the resonant frequency and the drill system capability must be ensured.