The invention relates to a harvesting machine for a root-tuber crop in a deep soil layer. Straight growing root-tuber crops, such as Chinese yam, are almost harvested by manual operation, so that the efficiency is low and the cost is high. The existing harvesting equipment has the defects that the soil excavating depth is shallow, and the crop completeness is difficult to guarantee. The harvesting machine comprises a power device, a machine frame, spiral drilling rods, a front conveyor, a conveying bet mechanism and a soil discharging auger, wherein side baffles are fixed to the two sides of the machine frame; the spiral drilling rods are assembled at the lower part of the front section of the machine frame side by side; the front conveyor and the conveying bet mechanism are assembled on the machine frame in sequence, and are joined and matched in tandem to convey and lift the harvested crop and soil to the ground; the soil discharging auger which is connected with the spiral drilling rods and the power device transfers power and evacuates the soil below the machine frame and pushed by the spiral drilling rods backwards. According to the harvesting machine, through mechanical soil loosening and through two-stage conveying of the front conveyor and the conveying belt mechanism, the soil excavating depth is increased, the work efficiency is improved, and the labor intensity and the operation cost of the crops, such as the Chinese yam, are reduced.