The heat distribution in the laser treated cancer tissue of the prostate was studied in this thesis in order to control the ablation thickness. Three types of lasers ( Nd: YAG , Ho: YAG , Thulium fiber ) were used in this theoretical simulation study. The absorbed laser energy by the prostate is different for each laser wavelength, which leads to different heat distributions in the prostate tissue and consequently different heat effects like ablation, coagulation, and hyperthermia. The thermal response of tissue is changing according to the change in the repetition rate (r-r) for a certain energy and pulse duration for the pulsed Ho: YAG laser and pulsed Thulium fiber laser. These variations were followed up to the carbonization state for 20 Hz and 40Hz (r-r) for three values of laser energies (60, 80,100) mJ, for each repetition rate of Ho: YAG pulsed laser, and three values of energies (40,60, 80) mJ for each repetition rate of Thulium pulsed laser. The ablation efficiency of 1.6w CW Thulium fiber laser was studied also. The geometrical shape of the prostate tissue was created by using the Gambit 2.2.30 program. The Fluent 6.3.26 program was used in this simulation to solve The radiation and energy equations which were used to find the heat distribution in the prostate tissue caused by laser . The result shows that the heat affected tissue surrounding the ablation zone by the Nd: YAG laser is large and the Nd: YAG laser needs higher energy to reach ablation compared with both of Thulium fiber laser and Ho: YAG laser which produce lower heat effects on the tissue that surrounding the desired ablation zone.The simulation results proved that the pulsed Thulium fiber laser is better to be used in prostate cancer tissue ablation as it produces minimum side effects on the tissue that is surrounding the ablated area.