Abstract: To a one--dimensional laser bar code scanner, by analyzing the longitudinal profile characteristics of the laser beam, and using convolution and Laplace transform, we obtain the exact expression of the Gaussian filtering effect which is generated when the laser beam scans the bar code images. And then we use the expression of the Gaussian filtering effect to design a Bessel filter, which can eliminate the Gaussian filtering effect and enhance the waveform edge. MATLAB is used to simulate the designed Bessel filter, the result shows that the filter improved the edge with no enhance of noise. That could be some reference value to improve the one--dimensional bar code signal.