The precision of manufacturing and installing together with the flexibility is a serious challenge for laser induced fluorescent detector (LIFD) of microfluidic chip. In this paper, a focus tunable liquid lens based on liquid zoom system for LIFD with automatic adjustment is proposed. With the help of liquid zoom lens whose surface curvature can be varied continuously by current, the system can achieve a continuous zoom. Instead of using the traditional mechanical axial displacement scanning motion mechanism, the proposed zoom system can implement axial displacement scan by means of the well-designed autofocus feedback current control function. The simulation results show that the focal length variation range of the designed optical system is 4.87mm～ 8.40mm, which is also the axial scanning displacement range. The size of scanning spot is around 15μm when a 473nm wavelength laser is used, which can meet the demand of microfluidic chip detection. With this design, the required precision of the LIFD could be reduced significantly as well as costs. Moreover, it also makes the detection of microfluidic chip qualified to adapt to different size of detecting channel.