A Grounded Coplanar Waveguide(GCPW) to slotline power divider is firstly built and verified based on the structural properties of both the GCPW and the slotline. Then an in-phase power divider and an out-of-phase power divider based on a GCPW-slotline-GCPW structure are designed according to the electric field distribution characteristics of the cross-section of the slotline. The simulation results show that the insertion loss of the in-phase power divider is better than 4 dB and the return loss is better than 9.6 dB in the range of 175~225 GHz; the insertion loss of the out-of-phase power divider is better than 4 dB and the return loss is better than 10.5 dB in the range of 185~215 GHz, and the amplitude imbalance is less than 0.24 dB and the phase imbalance is less than 1.3 °. Compared to other terahertz power dividers, the power dividers presented in this study are simpler, more compact, and easier to integrate, with comparable insertion and return losses.