The present invention discloses a fluidic mixer of serpentine channel incorporated with staggered sudden-expansion and convergent cross sections, which comprises a flat cover and a channel body. The channel body further comprises two L-type mixer inlets, a mixing channel, and two L-type mixer outlets. The configuration of the mixing channel is a single serpentine channel incorporated with staggered sudden-expansion and convergent cross sections, wherein the serpentine structure and the sudden-expansion cross sections induces split flows, which further enable the fluid to stretch and fold so that the contact area within the fluid can be increased. The convergence after sudden expansion in cross section is to prepare the next action of sudden expansion, and such an iterative structure can obviously enhance the mixing effect. The present invention has the following characteristics: planar structure, which enables the measurement and fabrication, particularly the fabrication of micro mixing channel, to be easily undertaken; L-type mixer inlets and outlets, which enables the connection between the mixing channel and external channels to be robust so that the linkage and encapsulation of the micro mixing channel will be advantaged thereby; single-channel design, which enables the flow resistance not to increase owing to the mixing action, and which also enables the working fluid to be able to involve two-phase fluids containing suspension solid particles; low pressure drop; and no bulb residence inside the mixing channel.