A hydrothermal processing method of fly ash generated by refuse-burning includes adding water in burning fly ash to form ash/water mixture, heating ash/water mixture to be boiled under atmosphere and adding solution of hydrazine material in boiled mixture then mixing them uniformly, making hydrazine material solution be reacted on with dioxin in fly ash and partial heavy metal ion be stabilized when temperature is up to preset degree and the temperature is held for certain period, cooling down and carrying out liquid-solid separation, using processed fly ash as construction material and discharging waste water directly out.