Hello karenzhaoyunlu,
Good day! Thank you for reaching out Surface Community. Surface devices are designed to work 0°C to 35°C. Keep your Surface out of the heat. I have few questions here to isolate the issue. I hope you don't mind.
Are you using the Surface branded power supply?
Are you using the Surface Device while charging or is it completely turned off?
How many hours when you notice it is very hot?
Try a Force Shutdown before charging the device to see if there are changes. Press and hold the power button until the screen turns off (about 10 seconds), then release the power button.
Looking forward for your response.
Regards,
KarenJune_F