Hot dry rocks are important resource for geothermal energy development. In this study, a novel technique to exploit hot dry rocks with circulating working fluid through a closed-loop in a horizontal well has been presented. A comprehensive wellbore pressure-temperature model has been established. Two typical heat transmission fluids, water and isobutane, are selected for comparison. The effects of the flow rate, the horizontal well length and the wellbore size on heat mining rate are analyzed. The power generation systems suitable for these two heat transmission fluids are compared. The simulation results indicate that a long horizontal well with a moderate mass flow rate can be applied for geothermal exploitation, and isobutane via a direct power plant has a better power generation performance than water through a binary power plant. In the case with water circulation at a mass flow rate of 3 kg/s, a net power of 143.5 kW can be obtained, while it can be increased to 258.1 kW with isobutane at a mass flow rate of 5 kg/s. Under different cost scenarios, the generalized unit cost of electricity generation can be reduced to 0.187 $/kW h when using isobutane with a reasonable low well cost and longer operation time. (C) 2019 Elsevier Ltd. All rights reserved.