I know that early z can be implemented in two ways.
the first by using two passes, and the second by sorting objects and rendering them from near to far.
But what I want to ask is:
1 Which way is unity used?
2 or is it unity that didn’t help us implement it, we need to implement it ourselves?
3 If we need to do it ourselves, who has an example
Object are sorted in a rough front-to-back order for the opaque queue by default: Unity - Scripting API: OpaqueSortMode
But I did an experiment, as shown in the GIF, where the green one was the first, the red one was the second, the yellow one was the third, and the blue one was the fourth, and unity didn’t sort them
Yes, rough front-to-back 
This means that objects are not guaranteed to be in a strict front-to-back order, but close to that.
I see. Thank you. I think it would be better for me to make a pre pass, so as to maximize the performance of early z.
I don’t think it’s possible in the built-in pipeline, but afaik Universal RP used to have it for shadows.
If you really really need it for built-in and you don’t have too many objects, you can sort them manually.
If I had the prepass or sort them manually, how can I see the effect, or the impact of these changes, for example, I switch to overdraw mode in the scene, then will there be a change in the picture
well, there should be a change in this mode, yes
I have sorted them manually, as shown in the GIF, but the overdraw diagram has not changed:(
Sorry, I thought it’s more useful than it is: SceneView "Overdraw" mode is misleading
Thanks, this link was useful for me and I found places to look at overdraw in renderdoc:)