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I found that many of atomic forces are larger than 0.001 eV/A in case of supercell (SC, 4x4) while all forces in primitive cell (PC) is lower than 0.001 eV/A when I performed geomoetric optimization for PC and use the results for positional input in SC for single-point calculation.
The forces in SC are shown below.

...
-0.018383 0.005499 0.092023
0.000000 0.074965 -0.003715
0.362168 0.156719 0.295411
0.000000 -0.390551 1.259424
-0.362168 0.156719 0.295411
0.000000 0.250426 -0.006243
-0.070366 -0.110111 -0.166424
...

I used the same method except for k-point mesh (24x1x24 vs 6x1x6) for SC (4x1x4) and PC.
I don't know why such deviation occurred. How can I obtain the reasonable forces i SC using the positional result obtained from PC?

Best regards,
Young

The volume of the cell is a parameter of your calculation.
When you change it the results are also changed.
Going to larger cells makes the relaxation more difficult.
Use more severe relaxation criteria.