To analyze the fast penetration of a 3D droplet into a granular medium and its flow, an optical measuring system comprising a laser, fluorescence, and a high-speed camera has been developed. The system consists of three parts: the penetration segment, wherein droplets contact a medium, adding index-matched fluids to reduce light scattering; the optical signal acquisition segment, which captures the liquid morphology in the medium at different conditions and performs a quasi-3D measurement using laser sheets; and the data processing segment, which analyzes experimental data. The moving distance, speed, and acceleration of the droplet in diverse directions at different times are measured to describe such dynamic process. Moreover, the data can support the establishment and verification of the dynamic theory, comprising force, momentum, and energy. The spatial resolution of this system is 0.02 mm, and its time resolution is 0.5 ms. They can address requirements such as real time, strong stabilization, and high spatial and desired time resolutions.