a cube below surface after "attach to motion path"
 

As picture shows:
I'm going to attach a cube to a motion path.

However, after I attached the cube to a curve:
the cube is below the surface....

what i can do to make it above the surface as before?

ThanksQ!

It looks like uit might ber due to the pivot point on the cube, try moving it to the bottom of the cube

Thanks! it works
However, how to adjust the pivot more exactly, like in autocad? by input numbers?

Thanks again!

You can move the pivot pint with snap tools or use the relative / absolute input funcions at the top of your screen. Absolute simply means it will position it at the specified point in world space while relative will off set it by specified units from its current position.

Because the move pivot tool is just like the translate took you could allways snap it in Y to the bottom of the cube by middle clicking the y axis to lock movement in y, and then holding down v to toggle vertex snapping on and snap it to one of the bottom verticies.

P.S.
Your resolution seems quite small so hide off the saving and snapping sections of your status line by clicking the dividers between them to reveal the numerical input line.