Self-priming　characteristic　of　5　models　of　shooting　flow　self-priming　centrifugal　pumps　with　inner　recirculation　installing　a　series　of　different　size　shooting　nozzles　were　tested.　Meanwhile,　the　vacuum　of　suction　pipe　and　impeller　inlet　was　measured　by　pressure　sensor　and　vacuum　instruments,　and　the　variations　in　vacuum　and　the　influence　of　cone　angle　and　outlet　section　area　of　shooting　nozzle　upon　self-priming　characteristic　were　analyzed.　The　result　shows　that　vacuum　of　impeller　inlet　determined　pressure　of　shooting　nozzle　outlet,　and　the　curve　of　vacuum　of　suction　pipe　displays　the　self-priming　progress　of　self-priming　centrifugal　pump.　An　optimal　cone　angle　of　shooting　nozzle　for　self-priming　characteristic　is　20°-30°.　There　is　a　relation　between　the　best　outlet　section　area　and　the　scale　of　self-priming　centrifugal　pump.　The　optimal　outlet　section　area　varies　according　to　exponent　relation　with　rated　flow　rate　of　self-priming　centrifugal　pump.