Abstarct: Droplet production in microfluidic devices has a wide range of application in biology, chemistry and medicine. Because of the wide spread use of this phenomenon several studies have been devoted to investigating various aspects of microfluidic droplet production numerically and experimentally. In microfluidic systems three major regimes of squeezing, dripping and jetting are identified for the droplet breakup. In flow focusing microfluidic devices the formation and breakup of the droplet appear more in the dripping and squeezing regimes than the jetting regimes. In present research the droplet formation and the droplet break up in flow focusing microfluidic devices for an immiscible flow is investigated numerically. Therefore, the level set method is used for the simulation of the interface tracking between two immiscible phases and the Newtonian and shear-thinning non-Newtonian fluids are investigated. The important dimensionless parameters of capillary number, viscosity ratio of two phases and the ratio of the inlet flow rate are investigated. Also the variation of the width of focusing channel (Hf), the variation of the size of the orifice, the exponent of carreau model (n) on the breakup droplet, the size of the droplet, the distance between drops, the droplet formation frequency and pressure distribution between phases. Obtained result comparison of numeric solution with available numeric and laboratory data indicates that obtained results have accuracy and reliability. The results show that, increasing the capillary number and ratio of the flow rate decreases the size of the formed droplets and the effect of these parameters is more significant in small values of capillary number and flow rate. In small values of capillary number, the possibility of the poly-dispersed breakup increases. The poly-dispersed breakup appears when the primary droplet is pinched off from the dispersed phase, the dispersed phase continues to grow side the orifice, forming secondary droplets until all the dispersed phase in the orifice are separated. The results of this study shows that, the effect of the variation of the width of focusing channel (Hf) on droplet size is more than the variation of the size of the orifice. In non-Newtonian dispersed phase, the exponent index has a significant effect on the droplet size. By decreasing this index, the size of droplets reduces and in small values of this parameter the poly-dispersed with several secondary small droplets appear. Also because of droplet formation poly-dispersed due to decreasing the exponent index, in pressure contribution diagrams between two phases, small variations observed in the last stage of droplet breakup process.