Photonic Network on Chip(PNoC) is a promising solution to overcome scalability and power consumption challenges in the traditional Network on Chip(NoC), with high bandwidth and low latency communication. Thermal sensitivity is one of the main problems in PNoC network. Because of the thermal sensitivity of photonic devices, thermal effects can cause the operation becomes incorrect or inaccurate, same as Laser power efficiency degradation, wavelength shifting, power loss due to wavelength mismatch, and switching disorders. Therefore, the goal of this study is set to present a suitable new mapping algorithm, which aims to Thermal distribution and maximum reduction thermal of PNoC. The main parameter that affects power consumption and thermal is a maximum power loss, maximum number of WDM channels and maximum communication thermal correlation. By increasing the amount of maximum power loss and the maximum number of WDM channels, the power of the signal in the source must be increased, which leads to an increase in thermal PNoC. In this paper, we modelled thermal parameters and suggested a fitness function to evaluate application mapping algorithms based on genetic algorithms. Based on evaluation results, the minimum thermal improvement is 23% in GA mapping with different W Coefficient and 46% improvement compared to the Nmap algorithm.