Thank's Tim.
Finally after several experiments, my wifi can connect as well.
Here step by step what I've done.
Turn off the wifi and cellular data.
Pull out the sim card.
Restart the ipad, then resetting the network (again).
Turn the wifi on, join my network. Connect ... try to browse my network and the Internet.
Turn on the cellular data.
Shut down the ipad, then inserting the sim card.
Turn on the ipad and voila ... carrier service and wifi signal shows in the upper left corner. Input the APN parameters.
Try the 3G connection by turn off the access point

Browse the internet, ok ... Then turn on the access point again. It can connect to my network again.