It　is　a　very　important　measure　to　give　privrities　of　developing　public　transportation　for　resolving　the　problem　of　traffic　jam　and　constructing　abstemious　urban　transport　system.　But　low　service　level　of　public　transportation　affects　its　appeal　to　citizens＇　travel.　Based　on　the　reliability　theory,　the　reliability　of　schedule　waiting-time　and　service　of　public　transportation　has　been　analyzed　from　different　points　and　the　correlative　model　has　been　made.