An engineering estimation method has been developed to calculate satellite attitude control thruster plumes at high altitudes, and the main exhaust gas species distributions are analyzed numerically. The grid generation technique is introduced to split the thruster nozzle exit section into cells, each of which is considered an independent point source, respectively. Hence, a modified free molecule model suitable for the nozzle exit local conditions is obtained. It consists of four primary formulae for density, mass flux, normal pressure and transitional energy flux, and three formulae for velocity, transitional temperature and internal energy flux. A nitrogen plume exhausted from a axisymmetric nozzle is firstly calculated. Numerical outlet conditions obviously influence upon analysis results for flow variables, especially, dynamic and thermodynamic variables. Then, an MBB 10N bipropellant thruster multi-species plume is investigated numerically. Comparisons are presented between the modified model and experiment, and good agreement is found for density distributions. Moreover, the levels of agreement are superior to those using the original single point source free molecule model. Pressure and internal energy vary more rapidly in the plume. It is unlike light molecule species that heavy molecule species mainly focus along the plume axis and their density distributions show a more dominant direction, i.e. axial direction.