An assembly of a lubrication system for fluid machinery includes a transmission shaft, an oil-injection insulating ring and a labyrinth ring. The transmission shaft defines axially power and passive sides. The power side includes a body unit having first and second bearings. The oil-injection insulating ring located between the first and second bearings sleeves the transmission shaft and connects a fuel-supply looping having outer and inner rings. The outer ring has at least one first hole communicatively connected with the fuel-supply looping. The labyrinth ring having first and second axial ends has outer diameters tapering from the second axial end to the first axial end. The first and second axial ends face the power and passive sides, respectively. A circumference of the labyrinth ring includes circular grooves to form a circumferential step-like structure. The labyrinth ring sleeves the transmission shaft and is embedded into the body unit.