A simple method to calculate measurement uncertainty by effective measurement points used quadratic interpolation is proposed. Curve fitting method was used to quadratic interpolation on typical fixed values. It resulted to quadratic interpolation function approaching the actual curve. Comparing with pointby point method, typical point method and stepwise method, it shows that measurement uncertainty by calculating quadratic interpolation approximate continuity, and can express the measurement uncertainty well over the entire range of value, overcome the serious misinterpretation of uncertainty, reduce the amount of computation effectively, represent calibration and measurement capability of measurement standard well.