What happens if I apply for Green card lottery game from USA and later I'm getting married to USA citizen ???

Hello: Your being very optimistic. However, if it is a bona-fide marriage and you qualify to adjust, you can go with the marriage petition. Regards, Brian D. Lerner Attorney at Law

While hopefully both your lottery entry and marriage work out well for you, trying both options should not be an issue if you wish. The initial application to be considered for the lottery is free and if you qualify this could prove to be a great route if you were to be selected. As things develop you could decide which you wish to use as your primary strategy, which likely would end up being through marriage in my experience. Consuting with an experienced immigration attorney to get legal advice as you plan may be helpful to you. Best of luck!

There is nothing inconsistent about applying for selection under the lottery and then applying for the green card based on a marriage to a US citizen. Unfortunately, you won't find out about whether you were picked for the lottery until after you are already married in February. You should consult with an immigration lawyer to understand the advantages of each.