Have you updated the watch to the latest version? And which device do you use to compare with? Please kindly send us some comparison screenshots about the altitude issue.
The watch displays altitude values based on air pressure readings taken by a built-in barometric pressure sensor. It comes with auto-calibration, which means that the watch calibrates itself with reference to a built-in GPS. This will save you from calibrating it manually.
Please help confirm which altitude is not accurate. At present, there are two ways to measure the altitude. One is in Compass widget, and the other is in Sports widget.
The Altitude During Exercise: Please submit a feedback (App➡Profile➡Feedback) from your Amazfit App, and send your Amazfit ID(App➡Profile➡Feedback➡User ID) here and also send us some screenshots of the latest activity including Details, Routes and Graphs.
The Altitude in the Compass: Please replicate the issue and then submit a feedback submit a feedback (App➡Profile➡Feedback) from your Amazfit App, and send your Amazfit ID (App ➡Profile➡Feedback➡User ID). And also let us know the exact time the issue happened.