Total　Suspended　Matter　(TSM)　is　one　of　the　significant　parameters　of　aquatic　ecological　environment　assessment.　It　is　necessary　to　grasp　the　dynamic　change　information　of　river　suspended　solids　concentration　in　time　for　inland　water　quality　monitoring　and　water　environment　management.　This　paper　is　based　on　field　measured　spectra　and　suspended　matter　concentration　data,　the　band　combination　reflectance　that　is　highly　correlated　with　the　concentration　of　suspended　solids　is　selected　as　the　independent　variable.　The　remote　sensing　inversion　model　of　suspended　solids　concentration　is　constructed　based　on　CatBoost,　random　forest,　and　multiple　linear　regression　algorithms.　In　order　to　determine　the　optimal　parameter　configuration　for　the　models,　the　grid　search　method　with　cross-validation　is　used　for　hyperparameter　tuning　of　two　machine　learning　models,　i.e.,　CatBoost　and　Random　Forest,　respectively.　And　the　inversion　accuracy　of　different　models　is　compared　to　determine　the　optimal　model.　Based　on　the　optimal　model,　multi-temporal　Sentinel-2　MSI　remote　sensing　images　from　2019　to　2020　are　used　to　invert　suspended　matter　concentrations　in　the　lower　reaches　of　the　Minjiang　River　and　analyse　their　spatial　and　temporal　variation　characteristics.　The　results　indicate　that:　b4/b3,　(b6-b3)/(b6+b3),　(b4+b8)/b3,　(1/b3-1/b4)×b5　are　the　best　band　combination　reflectance　for　MSI　inversion　of　TSM　concentrations　in　the　lower　Minjiang　River;　Compared　with　the　other　two　models,　the　suspended　matter　concentrations　inversion　model　based　on　CatBoost　algorithm　with　hyperparameter　optimized　has　the　highest　accuracy,　with　a　coefficient　of　determination　R2　of　0.95,　Root　Mean　Square　Error　(RMSE)　and　Mean　Absolute　Percentage　Error　(MAPE)　of　15.32　mg/L　and　19.68%,　respectively;　The　distribution　of　suspended　matter　concentrations　in　the　lower　reaches　of　the　Minjiang　River　from　2019　to　2020　is　＇low　in　the　west　and　high　in　the　east＇,　with　a　rising　trend　from　Baisha　to　the　mouth　of　the　Langqi　inlet;　The　suspended　matter　concentration　is　highest　in　summer,　followed　by　winter　and　autumn,　and　lowest　in　spring.　This　study　provides　an　effective　technical　means　and　theoretical　reference　for　the　monitoring　and　spatio-temporal　variation　analysis　of　suspended　matter　concentration　in　the　lower　reaches　of　Minjiang　River.　©2022,　Science　Press.　All　right　reserved.