Junction temperature and carrier temperature are widely concerned as significant parameters affecting LED luminous efficiency. The variation rules of electroluminescence (EL) spectrum and carrier temperature with junction temperature of GaN-based blue micro-LED were investigated in this paper. The accurate real-time measurement of junction temperature and EL spectrum of GaN-based blue micro-LED at current densities of 0.04~53.4 A/cm2 were conducted by using the chip design with a built-in integrated sensor unit, and the range of the low-temperature end of the junction temperature measurement was extended to 123 K using the forward voltage method. The results show that the linear slope of junction temperature and forward voltage change due to carrier leakage and series resistance at low temperature. The high-energy slope method was used for EL spectrum to calculate the carrier temperature at different current densities. It is found that the carrier temperature and junction temperature can be approximately fitted by a quadratic equation within the range of junction temperature and current density under study. And the law of the variation of the carrier temperature with junction temperature and current density was analyzed and explained.