A novel compact triple-mode triple-band bandpass filter (TB-BPF) based on equilateral triangle substrate integrated waveguide is first proposed. The first passband response is achieved by the fundamental modes of the first and third cavities. To obtain the second and third passbands, a new postperturbation method is proposed. And based on it, the perturbed TM101 and TM201 modes of the second cavity can couple with TM102 modes of first and third cavities via inductive window, respectively. By adjusting the width of the inductive window, the second and third passbands can be achieved. Source-load coupling and complementary split-ring resonators (CSRRs) are introduced to produce transmission zeros (TZs). Total eight TZs are obtained, which highly improve the performance of the out-of-band. Finally, a TB-BPF is designed, fabricated, and measured. The simulated and measured results show good agreement.