Sleeve grouting defects are one of the common issues in prefabricated structures, which may pose serious safety hazards to buildings. To investigate the effect of high temperature on the mechanical properties of defective grouted sleeve connections, a uniaxial tensile tests considering temperature (20~600 ℃, defect location: (compaction/horizontal), and defect degree (10%~20%) was designed to reveal the failure mechanism under the synergistic action of high temperature and defects. The test results indicate that under high-temperature conditions, steel bar fracture and pull-out are two typical failure modes. Specimens with compactness defects (with a 20% defect degree) already lead to pull-out failure even at 20 ℃. As temperature increases and defect severity worsens, the ultimate bearing capacity of specimens decreases, with a reduction of 30.21% to 47.33% under 400 ℃ conditions. The yield plateau of the load-displacement curve exhibits a degradation process characterized by increasing slope until it disappears. Based on experimental data, an evaluation framework for connection performance at high temperatures was established: an exponential connection performance calculation model was proposed through the evolution laws of yield ratio, strength-to-yield ratio, and ductility ratio. A bond stress prediction model was derived for sleeves with grouting defects at high temperatures to achieve prediction of bond strength. The synergistic effect of temperature and defect degree significantly weakens the bonding performance between the sleeve and grouting material, and the specimens with density defects are more sensitive to high temperatures than those with horizontal defects.The research results provide theoretical support for fire-resistant design and quality assessment in prefabricated construction.