Abstract: As a new optical element, the liquid lens provides adjustable optical power by changing the curvature. The transmission wavefront quality of liquid lens will affect the imaging quality. In order to apply liquid lens to precise optical system, it is necessary to investigate its transmission wavefront characteristics. The variation of the optical path difference (OPD) with the curvature radius, and the sensitivity of the OPD to the optical power in different heights of incident light in liquid lens aperture were analyzed by theory and simulation, so as to study the uniformity of slight variation of OPD in pupil. The transmission wavefront of liquid lens in zero, positive and negative optical power was measured. The uniformity of OPD variation of liquid lens was verified by analyzing the experimental data. The experimental results show that the spatial maximum difference of optical path difference variation is about 0.22 λ~0.36 λ, and the dispersion degree of spatial distribution is about 0.01 λ~0.02 λ. The analysis results show that the OPD variation of liquid lens with respect to the minor variation of electrical current has good uniformity, which can provide support for application and aberration compensation of liquid lens in precise optical system.