This paper measured and studied the reaction force of blasting erosion arc machining (BEAM) of SiC/Al based on a piezoelectric sensor. The characteristics of the reaction force waveform was discussed, and the forces in different dielectric are compared. Then, the frequency characteristics and the relationship between reaction force and discharge parameters (pulse on time, current and open voltage) were researched. Furthermore, the influence of relationship between reaction force and the material removal mechanism of discharge processing was discussed. And finally, a method to reduce the reaction force during BEAM of thin-wall SiC/Al workpiece which is commonly used in aerospace industry was given.