Learning is a process that occurs in education, including formal and informal education. The learning process requires assessment to determine the choice of appropriate learning methods. In addition, there are two student errors in solving math problems, namely mathematical processing errors and conversion errors. At the same time, errors in mathematical processing are greater than other errors. Problem transformation (transformation), which is the process by which students transform mathematical problems into the forms of mathematical models, trying to find the relationship between what is known and what is needed, the next step. This study uses descriptive qualitative research methods to know the difficulty of Mathematics Tadris Study Program students of State Islamic University Syekh Ali Hasan Ahmad Addary Padangsidimpuan in solving geometry transformation problems. The question difficulty is the difficulty in starting a solution. There are two types of problems in the proof of the geometry of transformation, namely the problem known definition of a mapping and the problem known formula for the results of a mapping. This study will discuss the difficulties made by students when solving problems that contain the definition of a mapping. In this study, in addition to analyzing the results of student test results, researchers also conducted interview tests. Based on the results of research and analysis conducted on students, it can be concluded that students have difficulty representing the definition of the solution of the problem and students have difficulty in determining the final result.