Displacement is a very important parameter in the civil engineering safety evaluation. But traditional displacement measurement methods are impractical and inconvenient in application, for the reason of money cost, time invested or labour involve. Spline-method is proposed to describe the displacement curve based on the angle values measured by inclinometers. Cubic spline is chosen for figuring out the inclination function and displacement values all over the structural. Numerical experiments have proved that Spline-method is feasible and has very high precision.