PdCoX (X=Si and Ge) alloys which are XYZ type half-Heusler alloys and also have face centred cubic MgAgAs-type structure which conforms to space group, have been investigated in different atomic arrangements which are called , and phases, using local spin density approximation in the density functional theory as implemented in VASP (Vienna Ab Initio Simulation Package) software. Both of the alloys are considered in ferromagnetic order. After the investigation of stable structural phase for these alloys, their full structural, electronic, magnetic, mechanical, and dynamical properties have been examined in this structural phase. The calculated electronic band structure and the total electronic density of states of our alloys indicated metallic behaviour. The estimated elastic constants show that these are stable and show anisotropic behaviour mechanically in and phases. Also, the calculated phonon dispersion curves show that PdCoX (X=Si and Ge) alloys are stable dynamically in the same structural phases.