In order to understand the mechanism of toxic effects of Cu²⁺ stress on the phycobionts of Ramalina sinensis，we studied the cell death of symbiont alga in the handsliced sections of the lichen thallus which were treated with 2 and 4 mmol/L CuSO₄ for 24 hours respectively by using two kinds of TUNEL reaction kit (Promega DeadEnd^TM Colorimetric TUNEL System and Roche in situ Cell Death Detection Kit). The results of the study showed: (1) the phycobiont cell vitality decreased significantly under Cu²⁺ stress detected by Evan’s Blue staining method. Moreover, there was a positive correlation between the cell vitality and the Cu²⁺ stress concentration and time. (2) When Promega DeadEnd^TM Colorimetric TUNEL System was used, the TUNEL positive phycobiont cells were 50.30% and 31.21%, respectively under 2 and 4 mmol/L Cu²⁺ stress conditions. The TUNEL positive cells of phycobionts were 53.17% and 36.88%, respectively when Roche in situ Cell Death Detection Kit was used under the same Cu²⁺ stress conditions, the results of both TUNEL kits was similar. (3) Considering the results of phycobionts cell vitality which was detected by Evan’s Blue staining method under Cu²⁺ stress, it can be concluded that apoptosis (programmed cell death) of R. sinensis phycobiont were induced under lower Cu²⁺ concentration (2 mmol/L) treatment, but the cell death of phycobionts were mainly caused by the necrosis and only few programmed cell death of the phycobionts was occured while the lichen was treated with higher Cu²⁺ concentration (4 mmol/L). (4) Both kinds of TUNEL detection kit can be used for the study of apotopsis of lichen phycobionts under heavy metal Cu²⁺ stress conditions. In addition, the handsliced sections of lichen thalli were used in this study instead of the paraffin sections. The experiment procedure was simplified by avoiding the complicated experimental steps. This research will be an important scientific reference for the further understandings of lichen responses to the various metal stresses.