I deployed it as docker image first, the uncontinuously lines came out and I thought it may be the heavy load.
Then I tried to deploy it to ESXi virtual machine and increased the CPUs&Mem, the same happened.
At the end, I run in VirtualBox, everything is perfect, the graph seems continuously.
Then I realized that my docker host is a ESXi vm. So I get to this conclusion: PMM-Server does not work well with vmware machines.
Prometheus fetches data every 1s from all mysql hosts, so it requires very good network performance and very fast VM reaction.
if ESXi has any network/CPU/memory delays Prometheus can ignores monitoring results.