This article aimed to study the efficiency and relationship between service quality dimensions of central library in Ferdowsi University by using Servqual Scale and Structural Equation Modeling. The method of this research is descriptive-survey. The statistical population includes all complementary education level students (postgraduate & Ph.D students). The random- classify sample method is used in this research. The validity of questionnaire approved by experts and the reliability of the questionnaire is %92 and it was calculated through Cronbach's Coefficient method. The findings of the present study shows that, there is a strong relationship between assurance dimension and service quality and little relationship between tangibles dimension and service quality.