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The subject of the graduate qualification work is “Analysis of an active low-pass filter using an operational amplifier”. Active filters are core components of modern signal processing chains,playing a crucial role in frequency selection in communication,measurement instruments,and other scenarios. This paper aims to achieve a 10MHz cutoff frequency and a 20MHz stopband attenuation ≥30dB, completing the theoretical derivation,parameter calculation,and simulation verification of a fifth-order Butterworth active low-pass filter. The study first outlines the Butterworth approximation characteristics,Sallen-Key topology principles, and the design logic of high-order filter cascades. Then,it constructs the circuit using a first-order RC section paired with two second-order Sallen-Key unity-gain sections.All resistors are uniformly selected as 1kΩ,and the capacitors for each section are calculated and selected with nominal values: first-order section 15pF,Q=0.618;second-order section C₁=12pF,C₂=18pF,Q=1.618;second-order section C₁=4.7pF,C₂=47pF.Frequency response simulations were performed using the Multisim platform with the high-speed operational amplifier OPA847. Test data show that the filters passband gain is close to 0dB, the attenuation at 10MHz is -3.56dB, and the attenuation at 20MHz is -29.47dB. All core performance indicators meet the design requirements. This design process and parameter scheme can provide a direct reference for the engineering implementation and experimental teaching of high-frequency active filters.