Student’s ability in mathematics is an important component regarding with their cognitive achievement. There is a general assumption among educationists that mathematics can develop people’s logical and analytical thinking. G.C.E. ordinary level exam in the Sri Lanka is an important stage to make a clear picture of student’s mathematical ability in Sri Lanka. Unfortunately, student’s results regarding with mathematics is so week in Sri Lanka. This study aimed to find the affected factors on student’s mathematics performance. This study has done as a case study in Passara educational zone, Sri Lanka. Multiple liner regression analysis used as the estimation technique. This study finalized that tuition class hours, education level of the most helpful person for student’s education at home and student teacher ratio at class room in school make significant effect on student’s mathematics performance. So, it’s clear that to improve the results regarding with mathematics in considering area should improve and provide the educational sources for students.