Abstract: Multi-line swinging reciprocating wire saw cutting is the main machining method to cut sapphire crystal bars into wafer substrate. The normal force is an important index to reflect the stability of the machining process. In this paper, the normal force Fn generated in the process of cutting sapphire crystal bars by a multi-wire swinging reciprocating wire saw was measured. The variation law of normal force at different positions and cutting depths was tracked. The variation amplitude of normal force Δ Fn  was used as an indicator to investigate the influence of various process parameters on the stability of the machining process. The experimental results show that the Fn corresponds clearly with the reciprocating motion of the wire saw and the swinging motion of the workpiece, and the Δ Fn in the front of the wire net is different from the middle and the rear area. Process parameters such as the speed of the wire saw (V_s), maximum swing angle (θ_max), single piece wire consumption (M_d), tensioning force (F_w), and total cutting time (T) have different effects on Δ Fn . The fluctuation degree of Δ Fn is closely related to the wear of wire saw.