Abstract: The dendrite growth behavior and solidification microstructure of high-carbon medium-manganese wear-resistant steel (medium-manganese steel) were systematically investigated by means of directional solidification experiments, metallographic microscopy, confocal microscopy, and theoretical calculations. The results calculated by Factsage 8.0 showed that the microstructural transformation of the medium-manganese steel was L→L+γ→γ, which belonged to the austenite solidification mode, with no peritectic reaction and no δ phase or other phases appearing. The directional solidification experiments showed that, under the experimental conditions (pulling speed from 5 μm·s⁻¹ to 300 μm·s⁻¹), the solidification structure of the medium-manganese steel exhibited a developed dendritic structure, and there was no cell-to-dendrite transformation during solidification. These results were consistent with the theoretical calculations. According to the directional experiments, the dendrite spacing of medium-manganese steel decreased as the pulling speed increased. Specifically, the average primary dendrite arm spacing (PDAS) decreased from 423.6 μm to 317.9, 258.9, 201.0, and 179.6 μm as the pulling speed increased from 5 μm·s⁻¹ to 50, 100, 200, and 300 μm·s⁻¹ respectively. Notably, pulling speed had a significant effect on reducing λ₁ at low pulling speed (5–200 μm·s⁻¹). However, this effect declined when the pulling speed was high (≥300 μm·s⁻¹). Meanwhile, the average secondary dendrite arm spacing (SDAS) sharply decreased from 110.38 μm to 59.77 μm as the velocity increased from 5 μm·s⁻¹ to 50 μm·s⁻¹ and then decreased more slowly to 45.0, 34.88, and 30.66 μm as the velocity increased to 100, 200, and 300 μm·s⁻¹, respectively. Therefore, compared with SDAS, PDAS in medium-manganese steel was more sensitive to the cooling rate. Moreover, when the pulling speed exceeded 200 μm·s⁻¹, both PDAS and SDAS changed little with further increases in velocity. The classical solidification theory models of Hunt, Kurz–Fisher, and Trivedi were used to predict the PDAS of medium-manganese steel. Compared with the experimental values, the comprehensive error rate of the Kurz–Fisher was the smallest, at approximately 17.95%. In addition, the Imagumbai, Furer–Wundelin, and Edvardsson classical solidification theory models were applied to calculate the SDAS of medium-manganese steel. Compared with the directional experiments, the comprehensive error rate of the Imagumbai model was again the smallest at approximately 13%. The PDAS and SDAS results predicted by classical solidification models did not fit well with the experimental results. This discrepancy may be related to the relatively high Mn and Cr contents in the medium-manganese steel. Therefore, to predict the PDAS and SDAS of medium-manganese steel more accurately, optimized models based on directional experiments were established. The relational expression between PDAS and pulling speed was Y=173.01+264.21e^(−X/86.77), with a regression coefficient of 0.999. In addition, the relationship between SDAS and pulling speed was Y=189.49X^−0.314, with a regression coefficient of 0.993. This research clarified the relationship between pulling speed and dendrite spacing in medium-manganese steel, providing theoretical guidance for improving the quality of medium-manganese steel, particularly in the development of continuous casting processes.