Hi Qianping,
You can display atoms from adjoining unit cells by clicking on the 'Boundary...' button at the bottom of the left sidebar and increasing the ranges of fractional coordinates displayed. That will work fine if you can select some values for the fractional coordinates which don't cut any molecules in half.
If your molecules overlap in space so that it's not possible to display the rest of the molecules from the first unit cell without also including parts of molecules from the second unit cell, you may be able to cut off unwanted bits of molecules using Cutoff planes, again on the 'Boundary...' dialogue.
Hope that helps,
Philip