Solution of the nonlinear vibration in conservation system by using the target function method is studied in this paper. The motion of pendulum is taken as an example problem. The relevant governing equation is integrated on the variable for time with the vanishing initial velocity and non-vanishing initial displacement. In this case, the velocity is a function of time, and it is in turn called the target function. Since the pendulum completes a periodic motion from the right side to the left side and then to the right side, the second zero of the target function becomes the period of the motion. In addition, in the time of numerical integration the displacement is also obtained. The suggested method depends on the numerical integration of the ordinary differential equation and the half-division technique for finding the zeros of a function. Solutions for some nonlinear differential equations are also evaluated. Finally, numerical examples and results are given.