my sd slot card of my mac don't work . i don't know why! can you help me

If it doesn't work with any sd card you insert into it then you can try a smc reset and a pram reset but if that doesn't work then the slot has failed. the only way to get that fixed is to replace the main circuit board, the logic board, which is very expensive. That is unless your mac still has a warranty on it then it would be free.

If you have no more warranty then just buy a sd card reader that connects to the computer by usb port.