The invention relates to the field of agricultural engineering, in particular to a diameter measurement device for a plant stalk. The measurement device comprises a measurement bracket, wherein two measurement probes are assembled on the measurement bracket, at least one measurement probe is a movable probe and a measurement position is formed between the two measurement probes. A drive device is connected on the movable probe in a transmission mode. A controller for driving the movable probe to move along the direction away from the plant stalk and setting displacement is connected on the drive device in a controlled mode. A pressure sensor is fixedly assembled on the movable probe and is used for providing working signals to the controller by sensing the pressure of the plant stalk to be measured. Displacement sensors of measuring the distance between the two measurement probes are further fixedly assembled on the measurement probes. Displayers are connected on the displacement sensors through analog-digital (A/D) conversion devices. In the process of measuring by the measurement device, the measurement probes just need to slightly touch the plant stalk to be measured, and therefore the plant stalk to be measured can not be damaged, and meanwhile measurement precision is guaranteed.