FDM printer first layer infill swell upward
Had tried below and didn't work:


Clean the bed
Use a brand new glue stick
Verify delta configuration and make sure z-plane is flat and parallel to bed 
Adjust z height to minimize the distance between nozzle and bed when z=0
Increase first layer extrude width


Printed again and watched carefully, then found that it was pull up because the printed PLA slice shrank. I realized that the problem was related to my change on the fan duct. Before, the fan blowed directly to the tip of nozzle; after changed it blows around.   

Tried to turn off the fan on first layer, the problem was solved. 

I suspect that the fan duct change made the extruded material not cooling down immediately. It shrank when the air blew on it. I need further test to verify it.