The 2022 extreme heatwave in Shanghai, particularly in the lower reaches of the Yangtze River Valley (YRV), was the strongest since 1961. This study examines the multiscale variabilities influencing this heatwave, focusing on Shanghai. The analysis reveals that about one-third of the 2022 heatwave days in Shanghai can be attributed to the long-term warming trend of global climate change. The heatwave was characterized by enhanced western Pacific subtropical high (WPSH) pressure and anomalous double blocking over the Ural Mountains and Sea of Okhotsk, leading to persistent high pressure over the YRV. The Pacific Decadal Oscillation and Atlantic Multidecadal Oscillation played significant roles in the blocking patterns, while interannual warming of the western Pacific warm pool and tropical North Atlantic favored the persistence of the double blocking and strong WPSH. Subseasonal variabilities, such as the boreal summer intraseasonal oscillation, also contributed by suppressing convection over the YRV. The study concludes that the 2022 extreme heatwave was a result of multiscale forcing, including climate warming trends and air–sea interactions at multiple time scales.The 2022 extreme heatwave in Shanghai, particularly in the lower reaches of the Yangtze River Valley (YRV), was the strongest since 1961. This study examines the multiscale variabilities influencing this heatwave, focusing on Shanghai. The analysis reveals that about one-third of the 2022 heatwave days in Shanghai can be attributed to the long-term warming trend of global climate change. The heatwave was characterized by enhanced western Pacific subtropical high (WPSH) pressure and anomalous double blocking over the Ural Mountains and Sea of Okhotsk, leading to persistent high pressure over the YRV. The Pacific Decadal Oscillation and Atlantic Multidecadal Oscillation played significant roles in the blocking patterns, while interannual warming of the western Pacific warm pool and tropical North Atlantic favored the persistence of the double blocking and strong WPSH. Subseasonal variabilities, such as the boreal summer intraseasonal oscillation, also contributed by suppressing convection over the YRV. The study concludes that the 2022 extreme heatwave was a result of multiscale forcing, including climate warming trends and air–sea interactions at multiple time scales.