Z Depth parameter can only be filled with an integer figure.
Can this z depth parameter of layer be set 1.500000 or other non-integer values ? I mean add this capability in the future version so that we can have 2D animation software with a nice 3D capability to enlarge and boost animation creation.
AFAIK, Z depth is a real value. I don’t understand what you mean.
-G
My purpose is trying to get 3D movement of camera, This morning, I read a wiki page, that is already possible in current synfig version: synfig.org/wiki/Multiplane_Camera
in synfig, nothing is impossible 
Yes, Z depth is most definitely a real number.
So if you had 3 layers and adjust the Z depth of the top layer of a canvas to say 0.2, then the layer dialog will show it as depth 0.2, above layer at 1, and layer at 2. And of course, if you made it 1.2, then it would be behind your 2nd object and in front of your third.
BTW - it looks like we have a bug as changing the Z depth of a layer in the params panel doesn’t update its value on the layer panel until the layer panel window gets focus. 
It is not a “bug” it is something not coded (call the rebuild layers routine when a zdepth parameter has changed)
-G
Sorry - missing feature. 
My fault, I don’t know why I considered Z depth is an integer type before. 