Developing　water-soluble　nanomaterials　with　high　photoluminescence　emission　and　high　yield　for　biological　analysis　and　imaging　is　urgently　needed.　Herein,　water-soluble　blue　emitting　silicon　and　nitrogen　co-doped　carbon　dots　(abbreviated　as　Si-CDs)　of　a　high　photoluminescence　quantum　yield　of　80　%　were　effectively　prepared　with　high　yield　rate　(59.1　%)　via　one-step　hydrothermal　treatment　of　N-[3-(trimethoxysilyl)propyl]ethylenediamine　(DAMO)　and　trans-aconitic　acid.　Furthermore,　the　Si-CDs　demonstrate　environmental　robustness,　photo-stability　and　biocompatibility.　Given　the　importance　of　the　potentially　abnormal　levels　of　acid　phosphatase　(ACP)　in　cancer　diagnosis,　developing　a　reliable　and　sensitive　ACP　measurement　method　is　of　significance　for　clinical　research.　The　Si-CDs　unexpectedly　promote　the　catalytic　oxidation　of　ACP　on　dopamine　(DA)　to　polydopamine　under　acidic　conditions　through　the　produced　reactive　oxygen　species　(ROS).　Correspondingly,　a　fluorescence　response　strategy　using　Si-CDs　as　the　dual　functions　of　probes　and　promoting　enzyme　activity　of　ACP　on　catalyzing　DA　was　constructed　to　sensitively　determine　ACP.　The　quantitative　analysis　of　ACP　displayed　a　linear　range　of　0.1-60　U/L　with　a　detection　limit　of　0.056　U/L.　The　accurate　detection　of　ACP　was　successfully　achieved　in　human　serum　through　recovery　tests.　As　a　satisfactory　fluorescent　probe,　Si-CDs　were　successfully　applied　to　fluorescent　imaging　of　A549　cells　in　cytoplasmic　with　long-term　and　safe　staining.　The　Si-CDs　have　the　dual　properties　of　outstanding　fluorescent　probes　and　auxiliary　oxidase　activity,　indicating　their　great　potential　in　multifunctional　applications.