Traditional　reliability　model　based　on　probability　has　been　applied　widely,　but　it　requires　overmuch　and　precise　data　to　describe　the　probabilistic　distribution　of　the　parameter.　In　practice,　there　is　often　not　enough　data　to　define　the　probability　model　precisely,　especially　for　the　design　of　water　hydraulic　pump.　Considering　that　the　design　parameter　Could　be　identified　as　intervals　in　water　hydraulic　pump,　a　non-probabilistic　reliability　model　based　on　interval　parameter　is　introduced　focusing　on　the　fatigue　strength　of　piston　and　valve　plate.　A　new　method　of　probabilistic　measurement　based　on　interval　index　has　been　proposed,　and　accordingly　the　ratio　between　the　mean　value　of　function　and　the　interval　width　is　defined　as　the　reliability　index　to　obtain　the　reliability　degree　of　the　hydraulic　component.　The　developed　non-probabilistic　reliability　model　is　applied　to　a　design　case　of　water　hydraulic　piston　pump,　and　the　reliability　analysis　is　conducted.　The　research　results　exhibited　the　high　reliability　of　the　water　hydraulic　piston　pump.　The　developed　non-probabilistic　reliability　model　could　mitigate　the　difficulty　of　obtaining　the　design　data　and　decrease　computation　effort　effectively.