Large different displacement results using beam elements and solid elements

The same geometry model. Two methods are used to calculate the displacement of the structures. The results are so different.

First method with the beam unit: 

-The same load:10000N

-Fixture: 4 joints

-Displacement 12.1mm

Second method with the solid unit: 

--The same load:10000N

-Fixture: 2 face

-displacement  23.6mm

Who can explain these?

Thanks!

Liu

SolidworksSimulation