Although Photonic Network-on-Chip (PNoC) has many advantages, such as high bandwidth and low delay, there is crosstalk when optical signals are transmitted by wavelength division multiplexing (WDM) in PNoC and the system performance will be further affected when the temperature changes. The crosstalk of optical signals in PNoC by wavelength division multiplexing is analyzed, and the influence of temperature on crosstalk noise of wavelength assignment is discussed. A wavelength assignment method based on improved ant colony algorithm is proposed. After the communication path between IP cores is established, according to the communication complexity between IP cores and the temperature distribution of the network, the number and spacing of wavelengths that each pair of communication nodes can allocate are searched, and the wavelengths are allocated to the communication nodes according to the objective function of minimum crosstalk . The experimental results show that the proposed wavelength allocation strategy reduces the crosstalk noise energy consumption by 25% on average compared with the traditional wavelength allocation strategy under different mapping models and network temperature distributions.