To solve the problem of weak signal to low volume fraction gases

field effect transistors（FETs）are adopted to amplify the signal of metal oxide gas sensors.FET is connected with the load resistor to form a new load

the total resistance of which is variable with the gate voltage of the FET

and thus amplifies the signal.The results show that the sensitivity is enhanced by 4～11 times

which is found to increase with the elevated measuring voltage.Simulated calculation of magnification mechanism and magnification factor are carried out using characteristic curves of the FET

and a toluene equivalent total volatile organic compounds（TVOCs）detector is developed.The detector shows variation trend of TVOCs accurately before and after an air purifier is opened

and source of error is analyzed.