I am planning to apply for Student Visa for USA . My parents who live in USA have their own business. I am wondering if I will be allowed to help in family business while my status in USA is a student.
F-1 students are not authorized to work. There are some exceptions for certain on-campus employment of 20 hours or less per week. There is also an economic hardship exception but that would require you to be a student for a full academic year and you would have to apply for the USCIS for an authorization. Consult an immigration attorney who will explain to you implications and requirements of working outside these parameters.
When you say help -- you mean work and get paid right? Off campus employment is not a "given" with a student visa. The rules vary -- you are talking about an F-1 student visa and not a J-1 exchange student program I would guess.
Better meet with a qualified attorney to see if/when you can get employment authorization from USCIS. Even if you want to "help" on a volunteer basis there are still rules to follow if you are going to stay in Immigration's good graces.