Driving　characteristics　of　planar　compliant　mechanisms　were　studied　based　on　the　pseudo-rigid-body　model　herein.　A　planar　four-bar　compliant　mechanism　was　taken　as　an　example　to　analyze,　the　pseudo-rigid-body　model　of　this　mechanism　was　developed　at　first.　A　new　method　for　calculating　the　driving　torque　was　then　obtained　based　on　the　dynamic　analysis　of　compliant　mechanism,　and　it　shows　that　the　flexible　hinges　have　impact　on　the　driving　characteristics　of　compliant　mechanisms.　The　results　of　example　indicate　that　the　peak　driving　torque　is　minimized　by　modifying　the　stiffness　and　the　unstrained　positions　of　the　flexure　hinges.