An apparatus and a method of indicating safety of a hydrogen tank when a vehicle fire occurs are provided. The apparatus includes a hydrogen storing tank and a thermal pressure relief device (TPRD) mounted within a valve of the hydrogen storing tank. In addition, a controller is configured to detect a flow rate of hydrogen discharged from the hydrogen storing tank, using a sensor to determine whether the detected flow rate of discharged hydrogen is within a predetermined reference flow rate range. The controller is also configured to transmit a warning signal when the detected flow rate of discharged hydrogen is included within the predetermined reference flow rate range.