The orifice which formed by the sudden change of channel’s scale on microfluidic chip and its application have introduced in this paper. The characteristics of orifice flow on microfluidic chip are studied by μ-PIV technology. The experimental PDMS chip is fabricated by hot press molding. The transient flow field experiment is carried out on the μ-PIV platform. The flow of thin-walled/thick-walled orifice was measured in experiment. There is flow constriction of orifice flow in jet state; the flow constriction of thick-walled orifice can pump the liquid in channel; and the critical Reynolds number of jet flow in microchannel structure is 190.