The present invention relates to a system and a method for controlling the thrust force of a belt of a CVT. The method includes: determining whether a rough road condition is satisfied; continuously calculating, in a case that the condition is satisfied, a thrust force for a first predetermined time by gradually increasing a safety factor to a safety factor of the rough road condition; increasing the thrust force of the belt to the calculated thrust force; and maintaining the thrust force according to the safety factor of the rough road condition for a second predetermined time. With that method, belt slip can be prevented and fuel efficiency can be improved.