In this study, a power cycle using carbon-dioxide as working fluid was designed. Thermodynamic analysis of a power generation system driven by a geothermal energy source was performed over the cyle. In the operation of cycle, geothermal energy was directly transferred to the working fluid and the applicability of the system proposed was investigated cycling the carbon-dioxide in the super-critical region. The results of the system were compared with those of a similar system present in the literature for verification. In addition to this, the results of the system which was designed assuming that thermosiphon effect would be sufficiently high to be able to cycle the working fluid were compared with the ones that were obtained using pump.