The major purpose of this paper is to illustarte of statistical design accuracy using trajectory simulation for launch vehicles design in conceptual design phase and also sensitivity analysis of velocity relative to effective external forces. Considering the advantages of statistical design to prevent the time and cost losses, system specification of sample launch vehicle calculated based on statistical data of the studied population. Then, by solving the equations of motion, design parameters are calculated in such a way that difference of the final velocity of trajectory simulation and needed orbital speed is less than 1 percent. Studied launch vehicles are two-stage liquid propellant vehicles, with Portability 2.5-3.5 tons mass to the low earth orbit. To validate, curves of speed, altitude and angle of path of launch vehicle designed with statistical method, compared with curves of Tsiklon launch vehicle, therefore correct operation the mission and accuracy of the statistical design algorithm is proved. By comparing ideal speed and speed of simulation, speed changes of any effective force obtained. Eventually speed loss factor at each stage and sensitive percent of each stage speed relative to the force, for both launch vehicles, statistical design and tsiklon, is analyzed.