python regular expression with utf8 issue

I got a file which includes many lines of plain utf-8 text. Such as below, by the by, it's Chinese.

PROCESS：类型：关爱积分[NOTIFY]   交易号：2012022900000109   订单号：W12022910079166    交易金额：0.01元    交易状态：true 2012-2-29 10:13:08

The file itself was saved in utf-8 format. file name is xx.txt

here is my python code, env is python2.7

#coding: utf-8
import re
pattern = re.compile(r'交易金额：(\d+)元')
for line in open('xx.txt'):
    match = pattern.match(line.decode('utf-8'))
    if match:
        print match.group()

The problematic thing here is I got no results.

I wanna get the decimal string from 交易金额：0.01元, in here, which is 0.01.

Why doesn't this code work? Can anyone explain it to me, I got no clue whatsoever.