The objective of the present research is to apply the Item response theory to verify the Validation of the achievement Test in science in the unit of “diversity and adaptation in the organisms” of the first semester, by identifying the psychometric characteristics of the achievement test, and the values of the difficulty parameter estimates, information function values at different levels of ability provided by the test, as well as the Item-Pearson Map for the achievement test, and the sampling of (100) pupils were chosen in a manner Random students in the first grade of preparatory school for the academic year 2016/2017 at Umm al-Abtall preparatory schools in Sharkia Government, to investigate the research tool, which is a test achievement in the science material in the unit (diversity and adaptation in the living organisms) for the first grade preparatory class "first semester" of the Year Study 2016/2017, according to Bloom's Taxonomy, the content of the Unit (diversity and adaptation in biota) of the science material for the first grade preparatory class "first semester" for the academic year 2016/2017 and planned by the Ministry of Education was analyzed and analyzed according to Bloom's Taxonomy The following: (Knowlege-understanding-application), the final sample of research was made from (183) pupils who were also randomly selected from the first graders of the academic year 2016/2017 at Umm al-Abtall Preparatory School in Sharkia Government, and applied the achievement test, and all The statistical analyses used in this research were made using the program (Winsteps 3.67.0), and it was concluded that the achievement test on an appropriate degree of reliability and validity, and the values of the difficulty parameter estimates, information function values at different levels of ability provided by the test, as well as the Item-Pearson Map for the achievement test were calculated.