This study aimed to determine the extent of relevance and reliability of fair value accounting to Combination Operations decisions by Knowledge Business Organizations with the presence of several approaches (ways) to measure the fair value of knowing that each entrance of which is given different values and requires the application of the terms of different possibilities, so you can choose the best approach for measuring the accounting operations integration of Knowledge Business Organizations , the problem of study in the following question what is the bestapproach to the fair value measurement when applying the purchase method of accounting measure for Combination Operations of Knowledge Business Organizations.The results of statistical analysis has shown that the cost approach is more approaches that affect the reliability of the financial, and the market approach is more approaches that affect the of the Relevance financial information.Finally, recommendations of the study The necessity of The balance between Relevance and reliability when application of fair value accounting .