Group-IV phosphides are relatively unknown materials as compared to the Group-IV carbide. In this work, we detailed the first principles calculations of the electronic and optical properties of the pseudocubic M(3) P(4) (M=Si, Ge, Sn) using the density function theory (DFT). Results are in good agreement with those previous works. Furthermore, the optical constants, such as the dielectric function, energy loss function and effective number of valence electrons are calculated and presented in the study.