how to import a planner project into project?

I realise this is 4 years old, but I thought it might help someone with this problem.

I had this exact issue, there is a way to do this. A helpful support chap at Microsoft helped me. Steps are:

Go to the Planner web page open the plan you want to import to project and get the plan ID from the URL and save that in notepad.

Next, go to your project environment and add this at the end of the URL:

/hubnew?importPlanId=[planid] 

replace [planid] with the code you copied earlier. 

e.g:

https://project.microsoft.com/[yourdomain]/en-GB?mkt=en-US#/hubnew?importPlanId=[planid]

This imports the plan into the project as a copy. The only issue is that it doesn't sync back to the planner; instead, it creates a copy of the plan, so you need to delete or not use the original planner item. I'm completely new to the project, so not sure if that is correct or not! But that was how I was told to get it working. 

Hope it helps.