A　portable　inspection　system　based　on　coplanar　capacitive　sensor　for　grouting　quality　is　presented.　With　the　derived　semi-analytical　equation　for　capacitive　proximity　sensor,　the　optimal　parameters　of　sensor　are　determined.　Based　on　the　principle　of　capacitive　proximity　sensor,　data　acquisition　unit　and　data　conversion　unit　are　designed.　To　promote　the　system,　system　control　unit　and　data　display　unit　are　designed.　According　to　the　approximation　theory,　the　system　verification　test　is　designed　by　measuring　capacitance　of　different　thickness　of　liquid　on　the　glass　surface　and　comparing　the　measurement　results　with　the　COMSOL　simulation　results,　data　processing　and　system　error　evaluation　are　done.　Experiments　show　that　the　average　relative　error　of　the　system　is　less　than　9.5%,　and　the　resolution　is　0.1mm.　In　addition,　the　inspection　system　volume　(except　the　coplanar　capacitive　sensor)　is　100mm×80mm×30mm.　The　experimental　results　illustrate　that　the　system　can　effectively　distinguish　the　stratification　of　grouting　in　the　ducts,　and　the　test　results　are　reliable　and　accurate.　©　2015　IEEE.