本文详细介绍了低通滤波器的数学模型及其滤波的仿真效果，而后介绍了对其进行数字化的过程，并给出了这种数字滤波器的PLC 程序，最后介绍了这种数字滤波器在低压铸造温度采样中的应用。应用实践表明，这种数字滤波的效果是相当好的。关键词：低通滤波器，模拟信号，低压铸造，PLCAbstract: This paper describes in details the mathematic model and simulating result of the low pass filter . And this paper discusses how to numbering the filter and make the PLC program of filter . Finally , the paper introduces the its application to low pressure casting temperature sampling . The practice result shows that the effect of numerical filter is quite good .Key words : low pass filter ; analog signal ; low pressure casting ; PLC