In this study, the electromagnetically induced transparency (EIT) of Pr³⁺∶Y₂SiO₅ doped photonic crystals in free space and confined systems of sandwich waveguides is theoretically investigated, and the influence of the confinement effect on EIT is revealed. Specifically, the influence of inhomogeneous broadening on the EIT of doped photonic crystals is thoroughly examined according to the semi-classical theory of light-matter interaction, and the conditions for the generation of EIT are obtained analytically. The validity of the theory is confirmed by comparison with experimental results. In addition, the EIT in a Pr³⁺∶Y₂SiO₅ doped photonic crystal sandwich waveguide system is further explored. The influence of the local electric field confinement effect on EIT is analyzed, and the conditions for the achievement of EIT in such a sandwich waveguide system are obtained in an analytical manner.