Climate warming is increasing the risks of extinction for many species. Giant panda is one of the most vulnerable mammals to climate warming due to its small population size and specialized diet of bamboo. Many studies have quantified projected habitat loss based on climate-change scenarios, but few have employed empirical data to investigate how the thermal habitat of giant panda has changed. In this study, we investigated the frequency, duration, and intensity of potential heat stress (PHS) occurrence that could surpass the biological threshold of giant panda by analyzing daily temperatures throughout the distribution range of giant panda from 1960 to 2010 and giant panda population survey data. We found an increase in the frequency of PHS25 (PHS above threshold of 25 °C) occurrence at a rate of 1.1–5.5 days/decade. The start date of PHS25 occurrence advanced at a rate of − 1.2 to − 4.6 days/decade, while the end date of PHS25 occurrence was delayed at a rate of 0.8–3.0 days/decade. The giant panda habitat is being exposed to an increased PHS occurrence. The area within reserves and densely populated giant panda habitat exposed to PHS occurrence expanded by 32–317% and 38–218%, respectively from the 1960s to the 2000s. Furthermore, PHS occurrence is intensifying; the annual accumulated degree-days of PHS25 and PHS30 occurrence (PHS above threshold of 30 °C) within the reserves increased by 39% and 140%, respectively. These results confirm that the potential threats to giant panda from climate warming are intensifying. It is urgent to expand the extent and range of giant panda habitat to allow giant pandas to move across landscapes in the face of ongoing climate warming.