Transmissions and resonant tunneling of superlattices composed of two alternating triangular photonic crystals (PhCs) and their corresponding effective one-dimensional (1D) superlattices are discussed. In the first case, below 0.40 ($c/a$), the transmissions of effective 1D superlattices calculated by the effective medium theory (EMT) match those of two-alternating-PhC superlattices calculated by the internal-field expansion method. No matter whether the propagating direction is along the symmetric (along $\mathrm{\Gamma }K$ or $\mathrm{\Gamma }M$ directions) or nonsymmetric axes (incident angle $\theta =45°$), the results hold very well. In the second case, resonant-tunneling phenomena and transmissions of the two-period superlattice composed of two alternating PhCs (the resonant-tunneling superlattice) can also be predicted by EMT below 0.20 ($c/a$). However, due to the evanescent waves at oblique incidence, the interface effect between two PhCs becomes explicit in the higher-frequency region and results in the deviations of resonant-tunneling frequencies in EMT calculations. By modifying the effective refractive indices of both PhCs, deviations are corrected and EMT calculations can exhibit resonant tunneling at right frequencies. Furthermore, the resonant-tunneling superlattice with larger background dielectric constant displays fewer modifications on the effective refractive indices.