...from the enviroment? Cats inside?

put his food in there, or throw a big bone to chew on for awhile.

Try putting his food bowl inside the dog house, when he gets hungry enough , he will get over his fear.

go into the doghouse if you can and lure him in .if possible .set with the dog and pet and talk to him when he see after a few times you arent scred he MIGHT start using it otherwise get him a doggie door

Cats and dogs can live together in harmony. It may take a bit, but I have a dog and a cat who have been housemates for three years. At first, the cat wasn't too sure about the invasion of his home, but the dog's attitude was 'cats are people too,' so it did not take too long for them to learn to tolerate each other. Now they even share a water dish..... sometimes at the same time!

Try putting his food inside the dog house. When he gets hungry enough, he will overcome his fear. Make sure that there aren't any serious problems between your pets. If the dog still refuses to go into his dog house, it may be because something happened the last time he went in one. If that is the case, let him in the house and get him one of those doggie beds and put it at the foot of your bed.