Objective To analyze deflection and forces of needle insertion and improve the inserting accuracy. Methods The measuring equipment was constructed with industrial camera, stepping motor and light source. The experiment of needle insertion into soft tissues was conducted with puncture needles having different diameters (1.3, 0.9, 0.6 mm), and the inserting forces at different puncture speeds (5, 10 and 15 mm/s) were measured by the force sensor. The needle deflection was obtained by digital image processing method. Based on the analysis of needle inserting forces, a projecting beam model was structured to predict the needle deflection. Results The deflections of puncture needles with diameters of 1.3 and 0.6 mm at puncture speed of 5 mm/s were predicted by using the projecting beam model. The absolute error was less than 0.5 mm, and the relative error was less than 10%. Conclusions The proposed model can predict the needle deflection effectively, which will provide references for the robot-assisted needle insertion.