With the constant hike in fuel prices on a day to day basis, maximum performance with minimum compromise on the front of fuel economy and emissions is highly desirable and expected from a vehicle's drivetrain. In this context, a drivetrain comprising a Continuously Variable Transmission (CVT) plays the role to the best extent possible. CVT facilitates a continuous change in gear ratios between the driver and the driven shaft. CVTs are superior to automatic transmissions with a fixed number of gear ratios in that it offers greater acceleration and more efficient fuel economy. In this paper, we propose to model a drivetrain of a vehicle comprising CVT. A detailed mathematical model based on the geometry of the components has been formulated and also, equations of their respective motions representing their behaviour have been derived. Furthermore, a dynamic model of a drivetrain, using bond graph method, is prepared which captures the behaviour of the CVT during the transient shift ratio condition and the complete simulation is implemented in MATLAB Simulink. The results substantiate the effect of mass of flyweights and spring constant of torsion springs on the performance of CVT.