Goodman furnace,his work,but gas valve dose not open,no heat

Working with a total lack of information on your part (no model number etc) the problem can be the control board or pressure switch.

I would test the pressure switch first since it is a cheaper than a circuit board. Naturally this is from an assumption the combustion air fan(the little fan in the front of the furnace) is running.

Since this furnace has many other controls depending upon the model I picked the two that usually cause problems. If you do not have a meter with which to test with and the knowledge to do the testing I suggest you call for On Site service from a professional since tools and knowledge are needed for testing purposes. If you just start replacing parts it can get real expensive.