The invention discloses a vacuum combined-type dynamic water silt model real-time landform measurement method and instrument, and the method comprises the steps: (1), determining a distance D1 from an ultrasonic detector to a communicating pipe bottom; (2), determining a distance D2 between a probe of a tracking-type water gauge and the communicating pipe bottom; (3), starting the tracking-type water gauge, starting a vacuum pump when the probe makes contact with a water surface, extracting air from a communicating pipe, and filling the pipe with water; (4), starting the ultrasonic detector; (5), recording the water levels QUOTE tau(t) tau(t) and water depths QUOTE Z' (t) Z' (t) at different moments at the same time, wherein the obtained water depth during ultrasonic measurement subtracts (D1-D2) is QUOTE (shown in the description); (6), calculating the water level and the riverbed landform changes. The method solves the following problems on the basis of the ultrasonic measurement technology: (1), reducing or eliminating the measurement blind region of the instrument; (2), achieving the landform measurement under a condition of a small water depth; (3), reducing or eliminating the impact of the instrument on a flow field and landform changes under the condition of dynamic water; (4), improving the landform measurement precision.