Abstract: Commonly, the roll-off factor of the stepped impedance low-pass filters is lower than 80 dB/ GHz and the stopband suppression is less than 20 dB, which limits its application. First, in this paper, a stepped impedance filter with wide stopband is analyzed and designed. Then, by introducing the fan-shaped stub to improve roll-off coefficient, a sharp roll-off and wide stopband microstrip low-pass filter with passband of 0-6GHz is designed. The filter is modeled, simulated, and optimized by using ADS and HFSS. Finally, the filter is fabricated on RO4003 plate and it is tested for verification. The measured results show that the 3 dB cut-off frequency is 6.02 GHz, the roll-off factor is 123 dB/GHz, the stopband is from 6.24 to 20 GHz, and the stopband suppression is greater than 30 dB.