Sleeve grouting defects pose significant safety risks in prefabricated structures. This study examines how high temperatures affect defective grouted sleeve connections through uniaxial tensile tests considering temperature (20-600°C), defect location (compactness/horizontal), and defect degree (10%-20%). Two failure modes were identified under combined thermal-defect conditions: steel bar fracture and pull-out. Specimens with compactness defects (20% degree) exhibited pull-out failure even at 20°C. Ultimate bearing capacity decreased significantly with rising temperature and defect severity, showing 30.21-47.33% reduction at 400°C. The load-displacement curves demonstrated progressive degradation as the yield plateau's slope increased until disappearance. An evaluation framework was established featuring: (1) an exponential performance model based on yield ratio, strength-to-yield ratio, and ductility ratio evolution, (2) a bond stress prediction model for defective sleeves under high temperatures. The temperature-defect synergy substantially weakened bond performance, with compactness defects showing greater thermal sensitivity than horizontal defects. This research provides theoretical support for fire-resistant design and quality assessment in prefabricated construction.