The invention relates to an oil-free planar sliding bearing with an extremely low friction coefficient, and further discloses a preparation method thereof. The oil-free planar sliding bearing with theextremely low friction coefficient comprises a carrier substrate and a self-lubricating alloy layer; the carrier substrate is made of steel; the self-lubricating alloy layer is manufactured with tinpowder, nickel powder, copper powder, iron powder and graphite powder as raw materials; the self-lubricating alloy layer is 0.5 to 3 mm thick; and pores of the self-lubricating alloy layer is filled with tetrafluoroethylene. The coating of the bearing is formed by compositely sintering iron powder, nickel powder, tin powder, copper powder and graphite powder, and thus the strength, pressure resistance and corrosion resistance of the bearing are improved. The bearing completely absorbs tetrafluoroethylene in a vacuum machine after being sintered, and is solidified in subsequent processes, so that the pores are permanently filled with tetrafluoroethylene, the self-lubricating property is achieved, the frictional loss is greatly reduced, and the friction coefficient reaches the optimal condition and can be as low as 0.025 or below.