A　photonic　microwave　down-conversion　approach　is　proposed　and　experimentally　demonstrated　based　on　a　Mach-Zehnder　modulator　paralleled　with　a　phase　modulator.　The　incident　radio　frequency　signal　and　the　local　oscillator　signal　are　feed　to　the　MZM　and　PM,　respectively,　and　these　two　modulated　optical　signals　interfere　in　the　coupler.　The　useless　higherorder　sidebands　are　removed　by　a　tunable　optical　band-pass　filter.　The　principle　of　microwave　frequency　down-conversion　is　analyzed　theoretically,　the　MZM　and　PM　paralleled　frequency　down-conversion　system　is　built.　Then　the　performance　of　system　is　tested,　and　the　experimental　results　show　that　the　spurious-free　dynamic　range　achieves　104.8　dB　u　Hz2/3.　Compared　to　the　conventional　MZM-MZM　cascaded　system,　the　SFDR　has　been　improved　by　16　dB.　The　MZM　and　PM　paralleled　frequency　down-conversion　system　can　balance　the　intensity　of　the　two　coherent　beams　easily,　and　only　single　DC　bias　is　needed.　The　proposed　method　possesses　simple　structure　and　high　dynamic　range.