A precise assembly mechanism contains: a control unit controlling a clamp unit, a loading unit, and a visual sensing unit to operate. The clamp unit includes a clamper and moves in a third direction Z, the loading unit includes a slider moving in a first direction X or a second direction Y, the holding tray moves in the first direction X or the second direction Y. The visual sensing unit includes a first sensor for identifying a position of an upper rim of each of at least one through orifice on a holding tray, a second sensor for identifying positions of a lower rim of each through orifice and a tip of each of multiple materials, a third sensor for determining a profile of each material in the second direction Y, and a fourth sensor configured to judge the profile of each material in the first direction X.