How can i get SDCard's infomation of M300 with IOS SDK? I tried to use DJICamera but it failed.

What kind of information are you trying to get off the SD card? ie - raw media, previews, storage state, etc?  
When you say you used "DJICamera " - do you have a code sample?  Did you use DJIMediaManager?

Here is a useful iOS Media Manager tutorial: https://developer.dji.com/mobile ... diaManagerDemo.html