This paper presents a new error analysis method based on the information theory. The analyse results of error of a digital measurement system will be illustrated more reasonably. This method is defined information theory combination, it will overcome the unintention between the uncertainty and the standard error of measuring results by traditional error analysis. On the basis of error spectrum analysis of sampling and quantization, an optimum digital filtering method is also presented in this paper. Simulation and testing show that the method is more resultful.