Mike Vick -- My Black Hair Brush Biz ... IS ON FIRE!!!

Mike Vick is like the black Paul Mitchell .. 'cause his black hair brush business is KILLING IT ... with demand for his WaveMasterz products higher than ever ... TMZ Sports has learned.

We broke the story ... Vick and Bow Wow got involved with the company last year after falling in love with the brushes.

Vick ended up buying 40% of the company. Bow Wow got 10%.

And the investment is paying off in a big way ... with WaveMasterz telling us the company is shipping out more than 500,000 brushes this holiday season to keep up with demand.

We're told the company only shipped out 3,000 last year ... when the company was in its infancy.

We spoke with Vick who tells us he's ecstatic about the growth -- saying, "I love the WaveMasterz brush ... it’s why I wanted to do more than endorse the brush, but be a part of this company."

He adds, "Now, we have to make sure the production keeps up with the demand because the response, even as we launch has been amazing."