As　an　emerging　technology,　fluorescence　immunochromatographic　assay　(FICA)　has　the　advantages　of　high　sensitivity,　strong　stability　and　specificity,　which　is　widely　used　in　the　fields　of　medical　testing,　food　safety　and　environmental　monitoring.　The　FICA　reader　based　on　image　processing　meets　the　needs　of　point-of-care　testing　because　of　its　simple　operation,　portability　and　fast　detection　speed.　However,　the　image　gray　level　of　common　image　sensors　limits　the　detection　range　of　the　FICA　reader,　and　high-precision　image　sensors　are　expensive,　which　is　not　conducive　to　the　popularization　of　the　instrument.　In　this　paper,　FICA　strips＇　image　was　collected　using　a　common　complementary　metal　oxide　semiconductor　(CMOS)　image　sensor　and　a　range　adjustment　mechanism　was　established　to　automatically　adjust　the　exposure　time　of　the　CMOS　image　sensor　to　achieve　the　effect　of　range　expansion.　The　detection　sensitivity　showed　a　onefold　increase,　and　the　upper　detection　limit　showed　a　twofold　increase　after　the　proposed　method　was　implemented.　In　addition,　in　the　experiments　of　linearity　and　accuracy,　the　fitting　degree　(R-2)　of　the　fitted　curves　both　reached　0.999.　Therefore,　the　automatic　range　adjustment　method　can　obviously　improve　the　detection　range　of　the　FICA　reader　based　on　image　processing.