Recently reported room-temperature ferromagnetic（FM）semiconductors Cd1-xMnxGeP2 and Zn1-xMnxGeP2 point to a possible important role of Ⅱ-Ⅳ-Ⅴ2 chalcopyrite semiconductors in “spintronic” studies. Here, structural, electronic, and magnetic properties of （i） Mn-doped II-Ge-VI2 (Ⅱ= Zn or Cd and V=P or As）chalcopyrites and（ii）the role of S as impurity in Cd1-xMnxGeP2 are studied by first-principles density functional calculations. We find that the total energy of the antiferromagnetic（AFM）state is lower than the corresponding FM state for all systems with Mn composition x=0.25, 0.50, and 1.0. This prediction is in agreement with a recent experimental finding that Zn1-xMnxGeP2 experiences a FM to AFM transition for T less than 47 K. Furthermore, a possible transition to the half-metallic FM phase is predicted in Cd1-xMnxGeP2 due to the electrons introduced by n-type S doping, which indicates the importance of carriers for FM coupling in magnetic semiconductors. As expected, the total magnetic moment for the FM phase is reduced by one mB with each S substituting P.