A novel micro-jet pump based on the principle of macroscopic jet pump are presented. The micro-jet pump can be used very easily for sampling in micro-fluidic systems under gas actuation. Vacuum suction mode provided by the pump can effectively decreases the formation of air bubbles and overcomes the interface tension between the liquid and solid wall in the micro-fluidic systems. Structurally the pump consists of a nozzle, a throat pipe and a pump chamber, which can be fabricated by means of silicon micro-machining technology. To obtain optimized parameters for the future designs, various pump configurations with different geometries were simulated through FLUENT, and the characteristics of the gas-actuated micro-jet pump was studied experimentally. The pump began to work at a threshold gas actuation pressure of 2 kPa, which can be realized easily by a medical syringe.