The backtracking mechanism is an important facility for logic programming. The backtracking itself is a good approach to obtaining all the possible solutions to a goal. On the basis of observing and studying the operating elements of backtracking mechanism in Visual Prolog with a group of instances, the four fundamental principles, i.e. those of bottom - up, right - left sequencing, rule matching and fact matching, are expatiated in detail. A backtracking approach implemented by means of repetition is explored. All kinds of possible cases in the course of backtracking are deeply analyzed and investigated, thus the essential characteristics and the applied fundamentals of the backtracking mechanism are revealed. Finally, the conclusion indicates that the backtracking mechanism has side - effects, and it is necessary to control carefully the searching courses by using a cut mechanism, a fail predicate and otherwise.