In order to truly reflect the flow characteristics of mercury droplet flow in varying-cross-section microchannel driven by inertia force, the impact of contact angle hysteresis on flow characteristics should be considered in numerical simulations. The VOF-CSF model of FLUENT software is used to study the flow characteristics of mercury droplet flow in varying-cross-section microchannel of micro fluidic inertia switch. Write the UDF of dynamic and static contact angle hysteresis,and simulate the flow characteristics in varying-section-mi-crochannel. The results show that the static contact angle and the contact angle hystersis of 10oare set in simulation, the acceleration threshold of micro fluidic inertia switch is 13. 2 gn and 16. 4 gn,respectively. The different contact angle hysteresis have an important impact on flow characteristics. The greater the contact angle hysteresis, the smaller the flow velocity of mercury droplet, and the harder mercury droplet breaks through the micro-valve and enters the reservior. Under the action of acceleration signal the contact line velocity of mercury droplet in varying-section-microchannel is lower, thus the effect of dynamic contact angle hysteresis on flow characteristics can be ignored and replaced by static contact angle hysteresis.%为了能更真实反映变截面硅微通道内惯性力驱动水银微液滴的流动特性，在数值仿真中应考虑接触角滞后对流动特性的影响。利用FLUENT软件的VOF-CSF模型研究了惯性微流体开关中水银微液滴在变截面微通道内受惯性力驱动的流动特性，编写动态和静态接触角滞后的UDF函数，对变截面微通道中内流动特性进行了数值仿真分析。结果表明，设置静态接触角和加载10º接触角滞后UDF函数时，惯性微流体开关的加速度阈值分别为13.2 gn 和16.4 gn。不同接触角滞后值对水银微液滴的流动特性有重要影响，且接触角滞后性越大，水银液滴流动速度降低，更难冲破微阀进入储液槽。由于水银液滴在惯性力驱动下的接触线运动速度较低，动态接触角对流动特性的影响可以忽略，动态接触角滞后可由静态接触角滞后代替。
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