Objective To establish the cutting force model of biopsy needle from the aspect of cutting mechanics and to reveal the relationship between cutting force of the needle and geometry of the needle tip. Methods Based on the traditional theory of metal cutting, a mathematical model of biopsy needle geometry was established. The needle cutting edge was divided into a series of elementary cutting tools (ECTs) with varying inclination and normal rake angles. The oblique cutting experiment was performed on the soft tissue cutting setup and a functional cutting force model was developed based on these ECTs. Results The force model could predict the cutting force of biopsy needle well. When the bevel angle ξwas 30°, 45° and 60°, the experimental forces of 18 G biopsy needle were 1.33, 1.38, and 1.56 N, respectively, while the predicted values were 1.29, 1.43, and 1.52 N, respectively. The relative error was less than 5%. Conclusions This cutting force model of biopsy needle quantitatively describes the relationship between the cutting force and geometry of the needle tip. The results can be used for the design and evaluation of new needle, and preoperative planning of needle insertion trajectory.