Hot air circulation heating method is adopted to heat the workpiece. Work, through the fan to external fresh air after mesh filter and heater to heat to the interior ministry, the workpiece heated by the outlet side, from the top after discharge, through the inner loop, in addition to breathe in a small amount of fresh air, most of the hot air heated by continue to use again, into the chamber, the chamber temperature gradually increases, When the temperature reaches the set temperature, the burner stops.