Abstract: While drilling of hot dry rock formations, drilling fluid may exert a cooling effect on the downhole rock at different temperatures, causing the changes of rock mechanical properties and failure modes. To investigate the influence of temperature and cooling on the mechanical parameters of hot rock, granite was studied. Acoustic and mechanical experiments were carried out on the heated samples (100–800 °C) after natural cooling and water cooling. The influence of temperature and cooling method on the mechanical parameters of granite was studied, such as acoustic wave velocity, compressive strength, elastic modulus, and Poisson’s ratio, etc. In addition, the macroscopic failure mechanism of rock under different treatment methods was analyzed. The results indicate that the mechanical parameters of granite gradually decrease when the temperature exceeds the critical threshold, with the most significant decrease of 23% occurring at 400 °C. The increase in temperature causes granite to exhibit ductile failure characteristics, resulting in a decrease in compressive strength. The compressive strength of granite decreases more significantly from 400 °C to 700 °C. The compressive strength of granite decreases by about 13% after water cooling compared to natural cooling. The study could provide a reference for the influence of drilling fluid cooling on mechanical parameters of rock and the calculation and analysis of formation parameters by acoustic logging in the drilling process of hot dry rock.