Well, do you have a trainer to help out with this? If you do, then ask her how to solve it too, but I know a few things you can do.
If your horse just wants to run at the fence at first, then do some small circles right at the moment when he gets fast. And you can half halt, making sure not to hang on his mouth either, because that can also get a horse wanting to go again.
When he wants to stop or go around the jump, look up-- look where you want to go. I have a problem with staring at the fence on my way to it, so make sure to keep your eyes up, shoulders back, and push him forward to the jump. If you keep your hands steady and keep your hands in front of you, your reins short enough, you also can create a "box" to drive him towards the fence. If you do this, you might actually literally feel like you put horse horse in a box, sending him straight to the jump!
I had to do this a couple years ago on a pony I rode a lot, and it really worked. I hope this helps, I just know a few things from having ridden many different horses before!