when I try to import file .mp3 ( my file is about 30 min ) I have this message :
import failed
this is likely caused by a malformed MP3.
Do you please any help? 
Audacity is more picky about MP3s than most applications but it also depends on the Audacity version so if you aren’t running the latest version (currently 3.0.5) try upgrading first.
Or see [u]this topic[/u] which has a couple of work-arounds.