Now we are on the process of converting a few of our ssrs reports into Power BI. I wonder if there any option to import an entire report structure(rdl files) into power BI. please help me with this
There is no such option. SSRS & Power BI are fundamentally different tools. If your SSRS reports are simple, then it shouldn't be hard to move the queries over to Power BI and then reproduce the same visuals (tables, charts, etc), though it would still look & feel very different.
Power BI has a focus on interactivity & data exploration that SSRS does not. As you convert reports, you'll likely want to update them to take advantage of features like slicers & cross-filtering & drill-downs.
On the other hand, SSRS has a lot of fine-tuning options that simply don't exist in Power BI (including an entire expression language). There are a lot of things you can do with SSRS that you can't easily recreate in Power BI (which is why a general conversion tool would be very difficult to write).