Python “Walk” directory to deal with xml

I'm a new comer about python, and I code this program to deal with xml in os.walk(). This program can print "channel code" from different xml files, and they all named "mmiap.xml".

It is the code:

#coding=utf-8
import os
import  xml.dom.minidom


path = "H:\\Dev\\CODE\\MMwithwalk\\"

for root, dirs,files in os.walk(path):

    dom = xml.dom.minidom.parse('mmiap.xml')

    root = dom.documentElement

    bb = root.getElementsByTagName('channel')   #Get channel code from mmiap.xml

    b= bb[0]

    print (b.firstChild.data)

After run this program, it shows "FileNotFoundError: [Errno 2] No such file or directory: 'mmiap.xml'"

What's wrong? It seems that traversal is not walk depth. But I can't find the problem.

PS: If I drag a mmiap.xml to root directory, channel code will be printed normally.