Soon I will take one year visa (I married with thai lady), but my question is:

For my work (import/export) I need to go to my country about 3 times a year. If I get one year visa and I need to go out Thailand: I will lose the validity of the visa or I can still use the same visa when I will come to Thailand again.

I mean: I can use the same one year visa several times?

If you mean the multi entry non immigrant class O visa valid for one year you are free to travel as it is "multi" entry. But if this has been extended in country on the basis of support (so you don't have to make visa runs) or employment you must obtain a re entry permit prior to any travel to keep the extension valid.

if this has been extended in country on the basis of support (so you don't have to make visa runs) or employment you must obtain a re entry permit prior to any travel to keep the extension valid.

If he intends to go out more than 2 times the multi-re-entry permit is cheaper.

Check the rpices with your local Immigration office.