The focus of this thesis is the design of a portable needle-free intramuscular injection device. According to pharmacology and nursing, the specification of the injection depth is set as 25 mm underneath the skin surface. Meanwhile, according to the fluid mechanics theory and the commercial product Medi-jector VISIONR, a model of the relation between piston pressure and outlet injection velocity is constructed and its accuracy is verified by measuring the outlet velocity and the output power of VISIONR. In respect of the difficulty of obtaining the human tissue, the test body of the anti-puncture property experiment is resorted to the porcine tissue. In order for investigating the anti-puncture property of the porcine tissue, the MTS Tytron 250 test machine is chosen to execute the experiment. Since the thickness of human skin and subcutaneous fat are lower than porcine tissue; and under the assumption that all the subcutaneous fat and muscle property of porcine are similar to human, including the penetration stress and the friction force during penetration. The human skin property, the porcine subcutaneous fat and muscle property are subjected to a human tissue geometry model for estimating the penetration stress of human body. Under the estimation, the penetration stress of human body is 71 MPa, which can be transformed into velocity form, 376.83 m/s, and the specification of the injection velocity is developed as 376.83 m/s.