<p>A three-dimensional flow-heat transfer-solidification coupled model was developed based on the finite element method to simulate the shrinkage cavity and porosity defects of a novel nickel-based cast superalloy K4800. The influence of pouring and preheating temperatures on shrinkage volume, Niyama value at the solidification front, temperature gradient, and cooling rate were investigated. Wire cutting experiments on ingots obtained by casting in molds made of 45-gage steel, which were then polished to capture images of shrinkage and shrinkage defects within them. By comparing the simulation results with this image, we found that the model has high accuracy, and the critical value of the Niyama criterion is determined to be 33.75 ( °C·s)^1/2/cm. The results indicate that the temperature gradient exerts a significantly greater influence than the cooling rate within the Niyama criterion. The effect of pouring temperature on the Niyama value is concentrated in the part of the ingot above 87 cm, and the effect of preheating temperature is negligible. Increasing the pouring temperature from 1400 °C to 1500 °C dramatically reduces shrinkage cavity volume, reaching its minimum at 1500 °C. The effect of preheating temperature on shrinkage cavity volume is significantly less compared to pouring temperature. The shrinkage cavity volume decreases only slightly with increasing preheating temperature, and its effect can be disregarded when pouring temperature is high. The comparison of shrinkage cavity volume values under different process parameters reveals that the volume is minimized at a pouring temperature of 1500 °C and a preheating temperature of 35 °C.</p>