Unsaturated　seepage　phenomenon　exists　widely　on　the　earth＇s　surface,　which　has　important　value　in　many　geotechnical　engineering　practices.　The　Richards　equation　describing　unsaturated　seepage　and　the　corresponding　definite　conditions　are　linearized　and　dimensionless　by　using　the　Gardner　exponential　soil-water　characteristic　curve　and　the　permeability　function.　Then,　based　on　the　principle　of　homogeneous　construction,　the　linear　dimensionless　seepage　governing　equation　is　equivalently　decomposed,　and　the　separation　variable　technique　is　used　for　analytical　calculation.　The　analytical　expressions　for　the　dimensionless　permeability　coefficient,　seepage　rate,　volumetric　water　content　and　matric　suction　head　are　obtained.　Two　typical　soil　layers　are　selected　as　the　research　objects　to　analyze　the　seepage　evolution　laws　under　the　sudden　increase　of　surface　infiltration　rate.　The　results　show　that　the　movement　speed　of　wetting　front　to　the　depth　of　soil　layer　decreases　gradually　with　time.　The　saturated　permeability　coefficient　of　coarse-grained　soil　has　a　significant　effect　on　the　development　of　unsaturated　seepage　from　steady　state　to　re-steady　one.　The　closer　to　the　surface,　the　shorter　the　time　required　for　the　seepage　velocity　to　increase　to　the　steady　state;　the　farther　away　from　the　surface,　the　later　the　response　time　of　infiltration　rate　to　the　surface　boundary.　The　vertical　distribution　of　matric　suction　head　and　volumetric　water　content　depends　only　on　the　boundary　conditions.　©　2023　Chinese　Society　of　Civil　Engineering.　All　rights　reserved.