On　the　basis　of　the　data　of　the　central　regions　of　Beijing,　through　researching　and　analyzing　the　causes　leading　to　the　crashes　of　vulnerable　road　users,　and　considering　the　characteristics　of　the　vulnerable　road　users,　the　concept　of　the　movable　obstacles　in　sight　was　used　firstly　and　it　provided　a　new　solution　to　the　prevention　of　crashes　of　vulnerable　road　users.　To　asses　the　frequency　and　severity　of　traffic　crashes,　the　concept　of　crash　severity　and　indexes　of　conflict　severity　are　proposed.　At　the　same　time,　a　model　for　predicting　crash　severity　is　established　and　it　is　helpful　to　predicting　and　estimating　the　situation　of　the　traffic　safety　of　the　vulnerable　road　users.