Needle-free syringe sprays liquid into the body tissues directly by ultra-fine, high-speed, high-pressure liquid flow. There are many kinds of needle-free injectors in the market currently, but most of them are very complicated and expensive. We designed the new kind of needle-free syringe driven by reluctance to improve the performance of existing electromagnetic needle-free syringes. This paper expressed how it works and established the mathematical model to analyze the relationship between force and displacement. Moreover, ANSYS was be used to simulate the distributions of magnetic induction lines. The simulation reveals that the core would stress a positive force before the middle point of the coil and the method to choose where to be served as the starting point of the iron core.