The invention belongs to monitoring methods and particularly relates to a uranium hexafluoride online monitoring method, which comprises the following steps of: 1, weighing; 2, flow calculation; and 3, comparison with a standard value: and comparing the flow obtained through calculation in the step 2 with standard flow, judging that an accident exists if the flow obtained through calculation in the step 2 and the standard value have larger deviation, or else, executing the step 1, namely weighing. The uranium hexafluoride online monitoring method disclosed by the invention has the obvious effects that the flow of uranium hexafluoride entering a reburner is determined by measuring the changes of the weight of a uranium hexafluoride container, so that a monitoring container cannot be corroded; in addition, the monitoring method can be used for monitoring the average flow in a period of time, so that a false alarm caused by instant high flow rate and instant low flow rate is avoided.