Abstract: Based on the characteristics of urban and rural bus services ,a diagnostic indicator system of urban and rural bus lines is built from the perspective of both bus passengers and companies .This paper extracts the principal com-ponents which show the urban and rural bus lines'physical ,operating and passenger flow characteristics .Then based on the results of hierarchical cluster analysis of urban and rural bus lines ,this paper establishes discriminant functions for different types of lines and builds discriminant function to diagnose urban and rural bus lines quantitatively .The field data are collected in Anning City and the 15 bus lines are divided into four categories of diagnostic types of urban and rural bus lines .The optimization scheme combined with the actual situation is put forward ,and the rationality of index system and the availability of the diagnosis method are validated .In conclusion ,this paper proposes a more accurate and effective di-agnostic method which combines qualitative and quantitative analysis .It provides a decision basis for optimizing adjust-ment of urban and rural bus lines .