The defective photonic crystals have wide applications. They can often be used to make optical devices such as resonators, polarizers, and filters. In this paper, the Petrov-Galerkin finite element interface method is proposed to calculate the band structures of multi-component defective photonic crystals, the defect states of photonic crystals with different component systems, geometric structures, interface shapes, material properties and modes were effectively studied. Numerical results show that the single point defect of two-component structure has little influence on the band gap, which only makes the waves continue to propagate in the local range, resulting in a defect band, while the multiple point defect makes the waves in a certain range propagate and multiple defect bands are generated. On the other hand, the line defect has a great influence, which makes the whole forbidden band disappear. When line defects are combined with point defects, the lateral point defects in waveguide structures can be advantageously used to induce narrow passbands within the stopband of photonic crystals or to induce narrow stopbands within the passband of waveguides. The three-component structure introduces inhomogeneous media, complex media shapes and different geometry structures. It is noticed that the media shape in the Ω3 region has limited influence on the results. The less smooth the surface layer is, the narrower the band gap is, and the high-frequency region in the TM mode of the n-type defect state is more likely to generate a band gap. For the TE mode, the n-type and v-type defect states are more likely to generate band gaps.