The　effects　of　surface　and　flexoelectricity　have　been　found　in　the　presence　of　strong　size　dependence　and　should　be　technically　taken　into　account　for　nano-scaled　dielectric　structures.　This　paper　proposes　a　Bernoulli-Euler　beam　model　to　investigate　the　electromechanical　coupling　response　of　piezoelectric　nanostructures,　in　which　the　effects　of　surface　elasticity,　dielectricity　and　piezoelectricity　as　well　as　bulk　flexoelectricity　are　all　taken　into　consideration.　The　governing　equations　with　non-classical　boundary　conditions　are　naturally　derived　from　a　variational　principle.　Then　the　present　beam　model　is　directly　applied　to　solve　the　static　bending　problems　of　cantilever　beams.　Without　considering　the　residual　surface　stresses,　the　bending　rigidity　can　be　defined　the　same　as　that　in　classical　piezoelectricity　theory.　The　bending　rigidity　is　found　to　increase　for　silicon　nanowires　and　decrease　for　silver　nanowires.　Also　the　flexoelectric　effect　in　piezoelectric　nanowires　has　a　momentous　influence　on　the　bending　rigidity.　The　residual　surface　stresses　which　are　usually　neglected　are　found　to　be　more　important　than　the　surface　elasticity　for　the　bending　of　nanowires.　However,　this　has　no　influence　on　the　effective　electromechanical　coupling　coefficient.　The　deflections　reveal　the　significance　of　the　residual　surface　stresses　and　the　bulk　flexoelectric　effects.　The　effective　electromechanical　coupling　coefficient　for　piezoelectric　nanowires　is　dramatically　enhanced,　which　demonstrates　the　significant　effects　of　the　bulk　flexoelectricity　and　surface　piezoelectricity.　The　effects　of　surface　and　flexoelectricity　decrease　with　the　increase　of　the　beam　thickness,　and　therefore　these　effects　can　be　ignored　for　large-scale　structures.　This　work　is　very　helpful　in　designing　cantilever-beam-based　nano-electro-devices.