This research is a descriptive qualitative study that aims to determine the ability of students to understand the system of three-variable linear equations problem through problem-solving instruction. The subjects chosen in this study were 6 students from SMA Srijaya Negara Palembang, consisted of 2 students with higher ability, 2 students with moderate ability, and 2 students with lower ability. The data was collected through test results and interviews then analysed descriptively. The results indicated that students were able to understand the problem and evaluate the obtained result. While students with lower ability struggled in using the substitution rule, therefore, could not establish the plan and solv the problem completely and correctly.