Abstract: Aiming at the excessive temperature interval between the zinc fixed point (419.53℃) and the aluminum fixed point (660.32℃) in the International Temperature Scale of 1990 (ITS-90), an Al-Cu fixed point (Cu 33wt%, 548.16℃) was developed as an auxiliary fixed point. Self-developed radiation thermometer RT9032 was used to test the melting and solidification temperature values of Al-Cu fixed points. For the determination of the Al-Cu fixed point temperature value, the average value of the melting plateau, the point of inflection (POI), and the upper limit (UL) temperature point were adopted. The research results showed that different determination methods do not produce significant differences for the melting temperature, with a maximum difference of 34 mK, and the repeatability of the Al-Cu fixed point is within 18 mK. Therefore, the Al-Cu fixed point (melting point) can be used as an auxiliary fixed point in addition to the ITS-90 fixed point.