pre:

I installed both python2.7 and python 3.70
eclipse installed pydev, and configured two interpreters for each py version
I have a project with some py scripts

question:
I choose one py file, I want run it in py2, then i want it run in py3(manually).
I know that each file cound has it's run configuration, but it could only choose one interpreter a time. 
I also know that py.exe could help you get the right version of python.
I tried to add an interpreter with py.exe, but pydev keeps telling me that "python stdlibs" is necessary for a interpreter while only python3's lib shows up.
so, is there a way just like right click the file and choose "run use interpreter xxx"?
or, does pydev has the ability to choose interpreters by "#! python2"/"#! python3" at file head?
I didn't understand what's the actual workflow you want...
Do you want to run each file on a different interpreter (say you have mod1.py and want to run it always on py2 and then mod2.py should be run always on py3) or do you want to run the same file on multiple interpreters (i.e.: you have mod1.py and want to run it both on py2 and py3) or something else? 
So, please give more information on what's your actual problem and what you want to achieve...

Options to run a single file in multiple interpreters:

Always run with the default interpreter (so, make a regular run -- F9 to run the current editor -- change the default interpreter -- using Ctrl+shift+Alt+I -- and then rerun with Ctrl+F11).
Create a .sh/.bat which will always do 2 launches (initially configure it to just be a wrapper to launch with one python, then, after properly configuring it inside of PyDev that way change it to launch python 2 times, one with py2 and another with py3 -- note that I haven't tested, but it should work in theory).
how to run python in eclipse with both py2 and py3?