I wanna to notify user task periodically, send email if it is not finished
You can attach a non-interrupting timer boundary event to the user task that goes to a task that sends a reminder e-mail. The timer expression can be repeated, see https://docs.camunda.org/manual/7.9/reference/bpmn20/events/timer-events/#timer-boundary-event and https://docs.camunda.org/manual/7.9/reference/bpmn20/events/timer-events/#time-cycle
This is an example of what it could look like.
https://cawemo.com/share/6627e174-6a83-48b7-a6e3-a9a7f0ba09f4