The main difference between the Huawei Watch GT5 Pro and the GT3 Pro lies in the technical functions and design. The GT5 Pro offers an elegant titanium case, improved health functions such as ECG and arterial stiffness measurement as well as more precise GPS technology. The GT5 Pro also has a more modern design and improved heart rate measurement. The GT3 Pro, on the other hand, has a slightly older design and less advanced health functions.

Some of the key differences are:
- Case material: GT5 Pro uses titanium, while the GT3 Pro may use other materials.
- Health features: GT5 Pro offers ECG and arterial stiffness measurement, which is not the case with GT3 Pro.
- GPS technology: The GT5 Pro has improved GPS technology that increases accuracy.
- Design and compatibility: Both watches are compatible with Android and iOS, but the GT5 Pro has a more modern design.