A novel design method for wide-stopband substrate integrated waveguide (SIW) bandpass filters (BPF) is proposed, which is realized by combining TE102- and TE101-based single-mode cavities with multiple-cross slots (MCSs). To demonstrate the proposed method, a planar SIW BPF with MCSs is proposed firstly. The ingenious MCSs have no effect on resonant modes, but have a great impact on non-resonant modes resulting in staggered their resonances. Thus, the stopband performance can be improved significantly and unload quality factors are not deteriorated simultaneously. To realize size-reduced wide-stopband SIW filters, a multiple-layer SIW filter is proposed on the basis of the planar filter. Finally, two SIW filters are fabricated and measured to verify the performance of the proposed SIW filters and the design method.