Necking　processes　of　the　droplet　generation　in　the　cross　junction　microchannels　are　experimentally　and　theoretically　investigated,　in　which　deionized　water　and　hexadecane　with　the　surfactant　span　80　are　used　as　the　dispersed　and　continuous　phases,　respectively.　Dynamic　mechanisms　of　the　neck　thinning　in　two　different　regimes　are　revealed　in　three　different　microchannels　with　width　ratios　of　1,　1/2,　and　1/3.　Characteristics　of　the　internal　flow　field　are　discussed　and　force　estimations　are　carried　out　using　the　velocity　information　by　MicroPIV　to　compare　the　varied　roles　of　the　shear　force　between　the　two　regimes.　According　to　evolutions　of　the　minimum　neck　width　and　the　thinning　rate,　the　necking　process　is　further　divided　into　different　stages　and　the　governing　driving　force　during　each　stage　is　confirmed.　Effects　of　the　flow　rates　and　the　cross-sectional　aspect　ratio　on　the　necking　process　as　well　as　the　neck　profile　at　different　stages　are　provided　in　detail.　The　distinct　features　of　the　two　regimes　in　the　squeezing　stage　are　well　captured　by　the　theoretical　estimations　of　the　effective　flow　rate　and　the　variations　of　the　actual　flow　rates　in　different　channels　are　reasonably　reflected　by　the　channel　width　ratio.　In　the　collapsing　stage,　the　quantitative　relation　between　the　minimum　neck　width　and　the　remaining　time　is　constructed　to　identify　the　physical　mechanism　and　the　self-similar　profile　is　compared　to　cases　in　the　open　environment　to　reveal　the　influence　of　the　confinement　in　microchannels.