Blac Chyna won't be prosecuted for allegedly brandishing a knife and threatening her hairdresser.
The Los Angeles City Attorney's Office tells TMZ the cases against Blac Chyna and her hairdresser were both rejected ... due to insufficient evidence.
The L.A. District Attorney had the first look at the case, but determined there wasn't enough there to charge Chyna or the hairdresser with a felony, so they gave the case to the City Attorney ... and now it's officially done.
Our law enforcement sources say the case was weak from the beginning.
TMZ broke the story ... BC and her hairdresser got into a heated exchange last month at Chyna's home in the San Fernando Valley. The hairdresser claimed Blac Chyna went after her with a blade and filed a police report, and BC appeared as a named suspect for assault with a deadly weapon.
Blac Chyna insisted she was actually the victim, not the aggressor ... and claims the hairdresser started hurling soda cans during the argument.