Set up a habitat for the snakes. These habitats should be separate and must be similar to ones in the natural environment.
Snakes are cold-blooded animals, so ensure that there is sufficient warmth available at the place where the snakes are kept.
In the habitat of the female boa, place a small heated rock in one corner. The rock should be constantly heated and to prevent the female boa from getting burned, wrap the rock in towels or any soft yet thick material.
Keep the snakes in their respective cages for a few months till the opposite sexes become accustomed to each other. Make sure that both the snakes are more than two years old.
Take the male boa out of its cage and introduce it to the female cage. If the living habitats are proper and there is no aggression, the snakes will mate.
Place the male boa constrictor back to its cage right after the snakes have mated with each other.
The female boa will resort to a warm spot after it has mated. Make sure the cage is warm enough for her to be comfortable. She will most probably spend a few days resting in one position.
Re-introduce the male snake weekly until you are confident that the female reptile has become pregnant.