Droplet　microfluidics　plays　an　essential　role　in　science　and　technology　with　various　applications　such　as　chemical　engineering,　environment,　energy　and　other　fields.　T-junction　with　a　constriction　microchannel　is　designed　for　the　controlled　production　of　monodisperse　microdroplets,　which　could　produce　droplets　with　the　same　size　under　a　lower　flow　resistance.　The　influence　of　the　microchannel　structure,　operating　conditions,　and　physical　properties　on　the　dispersion　rules　is　systematically　investigated　by　combinations　of　micro-particle　image　velocimetry　(Micro-PIV),　high-speed　camera　and　numerical　simulation.　Compared　to　the　traditional　T-junction　channel,　the　T-junction　with　a　constriction　microchannel　can　generate　smaller　droplets　whose　size　conforms　to　the　size　prediction　formula　of　the　traditional　T-junction　channel.　It　is　found　that　the　velocity　vector　of　the　T-junction　with　a　constriction　microchannel　is　faster　than　that　in　the　T-junction　channel　at　each　stage　of　droplet　generation.　The　droplet　size　is　mainly　based　on　the　Ca　number,　the　flow　rate　ratio　and　viscosity　ratio　of　the　continuous　phases　in　our　channel,　and　the　range　of　the　index　of　Ca　with　the　droplet　size　is　found.　The　constriction　width　has　a　significant　influence　on　the　dispersion　rule,　as　there　is　a　decreasing　tendency　for　the　droplet　size　with　reducing　constriction　width.