Abstract: Convolution integral and convolution summation play an important role in the analysis of the linear time invariant systems. At present, many text books have published in my home country or foreign country , especially the ?sSignals and Systems?t all discuss the methods by use of the graph to determine the up limit, low limit and the interval of exist of the convolution integral or convolution sum. Based on which, we present a compact formula to evaluate the convolution integral and convolution summation. So that, the convolution integral and convolution summation be computed directly according to the definition and the complexity of the compute process be simplified.