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,K_{40 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.