This paper proposes an analytical model to describe rock drilling processes using drag bits and rotary drills, and to induce relations among rock properties, bit shapes, and drilling parameters (rotary speed, thrust, torque, and stroke). In this model, a drilling process is divided into successive cycles. Each cycle includes two motions: feed and cutting. According to this model, drilling torque includes four components generated from cutting, friction, feed, and idle running respectively, the first three items are all proportional to the uniaxial compressive strength (UCS) when the penetration rate is constant. Laboratory tests verified the correctness and effectiveness of the proposed model qualitatively. Especially, the influence of friction on the flank face and the idle running was confirmed. Field experiments were performed. The results showed good correlation between the torque, penetration rate, and UCS. The proposed model and equations engender the possibility of eliminating useless components of cutting forces when investigating the relation between mechanical data and physical properties of rocks.