Primary purpose of this article is to Discuss and Analysis on Curve Fitting and Spline Interpolation. Here explain Spline Interpolation with mathematical examples. Spline interpolation is a sort of polynomial interpolation where the interpolant is usually a piecewise polynomial called spline. Which means between two points we have a piecewise polynomial curve which joined smoothly towards the neighbouring curves. Cubic spline provides different important applications. One of several important application is with Computer graphics.