To　evaluate　the　spatiotemporal　evolution　of　pore　water　pressure　in　unsteady　seepage　flow　ahead　of　a　tunnel　face,　a　partial　differential　equation　for　unsteady　seepage　is　established.　The　ranges　and　boundary　conditions　of　the　unsteady　seepage　flow　are　specified,　and　the　analytical　solution　of　the　unsteady　seepage　flow　is　obtained　by　the　eigenfunction　method.　The　obtained　analytical　solution　additionally　considers　the　time　factor,　which　can　be　used　to　study　the　influence　of　seepage　time　on　the　seepage　flow.　And　the　pressure　transmitting　coefficient　is　introduced　to　analyze　the　influence　of　water　and　soil　characteristics　on　the　unsteady　seepage.　The　analysis　shows　that　the　spatiotemporal　evolution　of　the　unsteady　seepage　flow　pore　water　pressure　ahead　of　a　tunnel　face　is　reflected　in　two　aspects,　the　dissipation　of　the　water　pressure　and　the　diffusion　of　the　influence　range　of　the　unsteady　seepage.　The　dissipation　captures　the　gradual　reduction　of　pore　water　pressure　at　a　specific　location　as　time　progresses.　Meanwhile,　diffusion　characterizes　the　alteration　in　the　spatial　distribution　of　water　pressure.　The　pressure　transmitting　coefficient　promotes　the　rate　of　unsteady　seepage,　while　the　height　of　water　table　has　a　greater　influence　on　the　magnitude　of　water　pressure　change　in　unsteady　seepage　flow.