A　multi-exponential　function　(ME)　is　proposed　to　depict　the　highly　nonlinear　soil　water　retention　curve　and　hydraulic　conductivity　function.　Then,　semi-analytical　solution　of　pore-water　pressure　in　an　unsaturated　infinite　slope　at　steady　state　is　derived　using　ME　to　depict　soil　hydraulic　properties.　The　solution　is　verified　with　experimental　and　numerical　results.　It　is　found　that　ME　can　better　describe　the　highly　nonlinear　hydraulic　properties　of　soil　than　the　single　exponential　function　(SE),　which　is　commonly-used　previously.　At　steady　state,　the　adoption　of　SE　results　in　overestimating　negative　pore-water　pressure　(PWP;　i.e.,　matric　suction)　by　about　25　kPa　and　slope＇s　factor　of　safety　(FOS)　by　100%　under　rainfall,　but　underestimating　negative　PWP　by　about　50　kPa　under　evaporation.　The　difference　between　PWP　and　FOS　calculated　by　using　SE　and　ME　becomes　more　significant　for　soil　with　bimodal　hydraulic　conductivity　function　than　that　with　unimodal　one.　This　difference　reduces　at　a　larger　slope　angle　and　deeper　depth.　Moreover,　this　difference　generally　increases　at　a　lower　SME/　SSE,　where　SME　and　SSE　represent　the　suction　at　which　the　unsaturated　hydraulic　conductivity　expressed　by　ME　and　SE　equals　the　applied　rainfall　intensity　or　evaporation　rate,　respectively.　When　SME/SSE　is　greater　than　0.1,　the　difference　basically　diminishes.