Is it possible for MPP students to apply for an econ PhD position? I'm an admitted master of public policy student at Harris School of Public Policy, U Chicago. I'm an international student from China and graduated from Peking University. My interested area is economic policy, and the reason I choose Harris School is the strong quantitative background and academic atmosphere. 

After being admitted, I start to think about the future career plan and what I really want. Not like the majority of MPP students who wants to work in the private or public sectors after graduation, I prefer applying for a Ph.D. in the econ or econ policy area. Less than 10 students will choose to continue a PhD at Harris every year. I know it's difficult because Harris is a professional rather than an academic school. But I still want to try and make some preparation before.

So could anyone guide me or give me some advice, please? Thanks a lot.
As you might guess, it is more common for a MPP student to apply to a Public Policy PhD vs a Econ PhD. However, you may be a candidate for the Econ PhD if you work the opportunities at Harris.

Like other PhD programs, Econ programs are looking for students who will be successful Economics researchers. You should try to get research experience at Harris and take the most quantitative classes possible. You may also need to take some advanced Math or Econ courses. 

The best way to prepare is to talk to faculty at Harris. You will especially want to discuss the situation with faculty who have PhDs in Economics.