This is bad, and means that the dog needs a teeth cleaning, it sounds like gingivitis, and your dog could lose his teeth if the tartar isn't removed; tartar causes the gums to swell and bleed if not removed. I've been using Petzlife, and it's said to prevent and remove tartar, but I don't know how advanced your dogs problem is. The Petzlife gel is said to soften tartar, and you then brush it away with your normal tooth brushing. You don't brush with Petzlife, but use it at a separate time. Here's the Petzlife site.
PetzLife Products Inc - Products For a Healthier Pet I also give Joey Bully sticks, as this helps scrapes the tooth surface while chewing.