Pycharm can not resolve packages in anaconda, but code runs fine

I'm reading python for data analysis. Now I have installed anaconda and pycharm on my Macbook Pro. I have also set interpreter in default settings and configurations with '~/anaconda/bin/python2.7'. I have wtitten the code:

import json
from pandas import DataFrame, Series

records = [json.loads(line) for line in open('usa.txt')]
frame = DataFrame(records)

results = Series([x.split()[0] for x in frame.a.dropna()])
print results[:5]

It works fine except that pycharm shows 'Unresolved reference pandas' and there is a red underline under pandas, DataFrame and Series. I have tried 'Invalidate Caches/Restart', but it doesn't work. Other packages in anaconda also can not be imported. When I import json, pycharm shows path '/System/Library/Frameworks/Python.f..'. I assume this is the problem. what should I do next?