在论坛上找到方法了，http://bbs.csdn.net/topics/340234292 

http://blog.csdn.net/junshao90/article/details/8215751

import subprocess

def main():
    process1 = subprocess.Popen("python  -u sub.py", shell=False, stdout = subprocess.PIPE, stderr=subprocess.STDOUT)
    #print process1.communicate()[0]

    while True:
        line = process1.stdout.readline()
        if not line:
            break
        print line

if __name__ == '__main__':
    main()

 

 

import subprocess
import time

p = subprocess.Popen('ping 127.0.0.1 -n 10', stdout=subprocess.PIPE)
while p.poll() == None:
    print p.stdout.readline()
    time.sleep(1)
print p.stdout.read()
print 'returen code:', p.returncode