Abstract: Objective 15Cr2Mo1 steel is pearlitic heat-resistant steel, which is widely used in electric power and petrochemical fields. However, problems such as cracks in some areas often occur during long-term use. Repair welding process has advantages of low operation difficulty, low cost and good resilience. The aim of this paper was to reveal effect of filling amount of repair welding on properties of welded joints. Methods Repair welding tests of 15Cr2Mo1 heat-resistant steel with different structure types and different groove types were carried out. Results The results showed that when grooves depth were 6.5 mm, 13 mm and 19.5 mm, each weld pass of repair welded joints were arranged reasonably and there were no obvious defects in each zone of welded joints. Under three kinds of filling amount, microstructure of weld in repair welded zone was austenite, and precipitates in grains were granular. A transition layer in fusion zone between original weld zone and repair welding zone was found with a width of about 15 μm. Line scanning results showed that a large number of austenitic elements Ni, Cr and Mn entered the zone, which increased hardening tendency of the zone. Conclusion Repair welded joints under three filling amount could maintain a good match of strength and toughness.