For the accurate calibrations of thermometers at low temperatures, triple points of oxygen and argon have been realized using sealed-type triple point cells. The triple points were realized with both adiabatic and continuous heating methods. The resistance of three capsule-type standard platinum resistance thermometers were measured at the triple points of oxygen, argon, mercury and water for the calibrations of these thermometers in the range from $-220^{circ}C$ to $0.01^{circ}C$. The extended uncertainty, with the coverage factor of 2, of the calibration in this range is smaller than 1 mK.