You can tell a surge brake system quite easilt. Look at your coupler
and see if there is an oversized 'box'.
http://www.championtrailers.com/techsup.html#techretro

Yes, I have checked my trailer, and it has an oversized coupler box.
And I have also checked under the trailer and see a wire going into
each wheel assembly. Now, I am sure that my trailer has a brake and it
is a surge brake.

Thanks for the picture.

Now, I have a question:
When I released the brake in the towing vehicle and started towing,
I often heard noise coming from behind me (likely coming from the
connection between the towing vehicle and the trailer). Is it a
standard behavior of a surge brake? May be the surge brake had engaged
when I stopped the car, and it remained engaged. When I released the
brake in the towing vehicle and stepped on the gas panel, the surge
brake could not respond fast enough to release its brake. That caused
the hitch ball of the towing vehicle to impact on the coupler of the
trailer, and this made noise. Is my understanding correct? If this
was the case, I should go easy on the gas panel when I go from stop to
start the vehicle.

Jay Chan