The active band-pass filter is designed by using the modern network theory and multinomial synthetic filter and by modulating and calculating repeatedly through the examination of charts. Its frequency-response curve and circuit structure completely satisfy the needs of various technical indexes. This paper discusses in detail the theoretical basis of the design from unit circuit to full-pole and multi-feedback filter network circuit,as well as the methods of calculating and debugging the parameters of various subbranch circuits. These circuit structures are simple and reasonable, and very easy to modulate and repair. Thus they replace the large-scale inductance and capacitance, and help miniturize the installations.