Maybe it's a full scale wind tunnel model. Is there any large wind tunnel facility in tianjin?
btw if it was a wind tunnel model they could still be early on in their project.
Looks like all control surface is absent on the thing covered, as well as the canopy, therefore the wing shape looks incomplete. Right now it could simply be the main body shell yet to be assembled somewhere else. Btw maybe this indicates that it will have all moving tail and horizontal stabilizers.
This is just one of those special days when you have something exciting and mysterious to look at.
It could be a wind tunnel model... but huitong mentioned this thing is due to fly in september some time, so we could be seeing parts for it getting all delivered together for reassembly at a different test facility to that which SAC usually use.
And the fact that the tails and stabilizers aren't attached to the fuselage is no indication of whether they will be all moving or not.