I have a fractured box falling in space, but in the POP network particle wouldn't emit from the surface of pieces when I choose Surfaces(random) in the “Emission Type” box, instead, they are emitting from the very center of the entire fractured box, forming a line straight down.
what's wrong? please help.

That is the nature of packed primitives, they are only points until you unpack them.

Inside your box_object1 drop down an unpack node after the dopimport1 and before the outt. Then you will see particles in places other than the zero axis.

If you use the Debris shelf tool you may get better results.

Again you solved my problem, Enivob, THANK YOU, GENEROUS GUY!