The cracking characteristics and the liquation cracking mechanism of laser additive repaired K452 superalloys are explored. The low-heat input pulsed laser process is used to control the generation of liquation cracks, and the microstructures and the mechanical properties of the repaired zones are analyzed. The results show that liquation cracks tend to be generated during laser additive repairing of K452 superalloys, which originate from the heat affected zone and extend to the repaired zone and the substrate along the grain boundaries. Under the action of tensile stress, the liquid films on the grain boundaries of the heat-affected zone become liquation cracks. The low-heat input pulsed laser process can effectively control the generation of liquation cracks. The average microhardness of the repaired zone of the pulsed laser repaired sample is 267.9 HV. The tensile strength and the yield strength are 814.3 MPa and 685.8 MPa, respectively, slightly larger than those of the as-cast substrate. The elongation is 4.87%, slightly smaller than 6.25% of the as-cast substrate. The low-heat input pulse laser process achieves crack-free slotting repair. The strength of the as-cast repair specimen reaches the strength standard of the as-cast substrate, and the elongation is slightly lower than that of the as-cast substrate.