Expertise is one of the proofs of the lawsuit and it is the expression of the opinion of an expert and a technical expert in relation to a subject that is completely within the scope of his expertise. This article, in a descriptive-analytical way, examines the nature, power and evidential value of expertise and also evaluates the possibility and impossibility of conflict between experts' opinions. For this reason, he first examined the conditions of the realization of the conflict between the proofs of the lawsuit and concluded that for the realization of the conflict, four conditions are necessary: the existence of at least two reasons, the incompatibility of the two reasons, the unity of the subject and the probative power of the evidence are necessary at the same time. Then, she evaluated the possibility or impossibility of realizing the conflict between the opinions of experts based on the above four conditions in different situations, and in the cases of the possibility of realizing the conflict, she provided a solution to resolve it.