[en] This paper aims to develop a phase-locked multicolor confocal micro-particle image velocimetry (PIV) technique to investigate the flow mechanism of microdroplet formation at a micro T-shaped micro junction. The object to be measured is a three-dimensional (3D) periodic multiphase flow with random disturbances, and this method is a solution for the 3D flow measurement of this complicated phenomenon. The phase-locking technique is needed to reconstruct the 3D flow field from the two-dimensional (2D) confocal micro-PIV measurement data. We successfully obtained each temporal phase of the periodic phenomenon noninvasively by detecting the passage of a droplet from the transmitted light of an optical proximity sensor. Then, the phase-locking technique also enabled us to select the same conditions of formation frequency, size, and translational velocity of droplets to minimize instability in the droplet formation phenomenon. The multicolor system can measure the dynamic behavior of each phase of a multiphase flow separately and simultaneously. As a result, the 3D flow structure of droplet formation was successfully reconstructed and investigated with high spatial and temporal resolution. (paper)