The influence of transition metals (Sc, Ti, V, Cr, and Mn) doping at different distances on the magnetism of CdS is studied by using generalized gradient approximation combined with Hubbard U in the VASP package. The results show that the doping systems are more stable, easy to form, and the wurtzite structure of CdS is not changed. It is found that the systems are antiferromagnetic (AFM) when nearest neighbor doping, which is attributed to the direct charge transfers between two impurity ions. The systems are ferromagnetic (FM) when the doping distance increases further, since the double exchange interactions are observed among the 3d orbital of the transition metal, the Cd-5s and the S-3p orbitals are at conduction band minimum. We also found that the total magnetic moment of each ferromagnetic system increases with the order of SC to Mn-doping, the spin polarizability of Cr-doping system is 100%. The estimated Curie temperature indicates that the Cr- and Mn-doped CdS in this paper can achieve room-temperature ferromagnetic characteristics, especially the Cr doping is the most prominent. And TM-doping does not destroy the semiconductor characteristics of the system. Therefore, the TM-doped CdS can be used as an ideal dilute magnetic semiconductor functional material. © 2020 Chinese Physical Society and IOP Publishing Ltd.