The invention discloses an automatic calibrating apparatus on a flow of a heat energy meter. The apparatus comprises a water circulation system, a data collection system and a control system. The water circulation system consists of a water outlet of a thermostatic water tank, a water pump, a vacuum tank, an inlet valve, a detected meter, a flowmeter, a flow adjusting apparatus, an observation window, a header tank, a draining valve, and a water inlet of the thermostatic water tank, wherein the above-mentioned components are communicated in order; besides, a heater is arranged in the thermostatic water tank. The data collection system comprises a multifunctional concentrator, a concentration meter reader, a temperature sensor, a pressure transmitter, and an electronic scale; and the detected meter and the flowmeter are connected with the concentration meter reader by the multifunctional concentrator. In addition, the control system is composed of a computer, an intelligent control instrument and a frequency converter; the heater, the temperature sensor, the pressure transmitter and the frequency converter are connected with the intelligent control instrument and the intelligent control instrument, the concentration meter reader and the electronic scale are connected with the computer. According to the invention, the apparatus has a simple structure; automatic control on calibration of a flow of a heat energy meter is realized; costs and an error rate are reduced; and an calibration efficiency and an accuracy are improved.