Abstract: Based on traditional step impedance filter, an improved design scheme of ultra-wide stopband microstrip low-pass filter is proposed. The sector microstrip structure is used as the low impedance line. Under the same filter's order, the proposed filter has a more compact circuit structure and better stopband characteristics than the traditional step impedance filter. The spurious passband has been suppressed by using parallel open circuit stub at the end of the filter to increase the extra transmission notch point. The structure of the filter is optimized by using ADS and HFSS simulation software, and physical processing and testing are carried out. The measured results show that the cut-off frequency of the pass band 3 dB is 2 GHz. The return loss is more than 20 dB in the 0-1.8 GHz pass bands, and the stopband rejection of the 3-20 GHz frequency range can reach more than 25 dB.