A low-pass transmission line structure with multi-level,tooth-shaped defects is proposed. The low-pass frequency and attenuation-band range could be effectively adjusted by varying the length of the branch of atooth-shaped defect. A wide-stopband filter with high out-of-band suppression was designed by cascading cross-coupled fan-shaped SIW filters using this tooth-shaped defect ground structure. Compared to traditional SIW bandpass filters, the rectangular coefficient,K40 dB, had a value of two, and the stopband range was greater than twice the center frequency, demonstrating good passband and stopband selection characteristics. The test results showed that the filters center frequency was 10.35 GHz, with 3 dB and 40 dB bandwidths of 507 MHz and 1.05 GHz, respectively. The insertion loss was better than 1.47 dB, which was consistent with the simulation results.