The purpose of this paper is to analyze the flow field on the propulsion nozzle of a micro-turbojet engine in function of the velocity. The 2D axisymmetric numerical simulation was made by using commercial software FLUENT?. A micro-turbojet engine was also employed for this study and it has the following characteristics: 100 N thrust, 130,000 rpm, mass flow rate 0.2650 kg/s, weight 1.2 kg. This engine is operating in Mexico city under the following conditions: P0, 78,000 Pa T0, 300 K, πc, 2.1 and a turbine entry temperature of 1000 K; it is considered that the nozzle is not choked. For this study, the viscous standard k- model, a semi-empirical model based on transport model equations for the turbulent kinetic energy (k) and its dissipation rate, is used. The transport model equation for k is derived from the ex-act equation, while the transport model equation for is obtained by using physical reasoning and bears resemblance to its mathematically exact counterpart. The employed grids are structured and the boundary conditions are obtained from a thermodynamic analysis. The results that are obtained show an increment of the velocity of 6.25% to the exit propulsion nozzle.