The invention discloses a control method for preventing the quenching oil of a diluted steam generation heat exchanger from entering a process water system. After high-temperature quenching oil rises to 1.2MPa through a quenching oil pump, and the inlet pressure of a heat exchanger is controlled at 0.5MPa by adjusting the opening of an inlet stop valve of the diluted steam generation heat exchanger; after the heat exchange of the diluted steam generation heat exchanger, the quenching oil returns to an oil washing tower through an outlet stop valve of the heat exchanger, and the outlet pressure of the stop valve is controlled at 0.4MPa; the pressure difference between the front of the inlet stop valve and the front of the outlet stop valve of the heat exchanger is controlled at 0.6-0.8MPa; the process water enters the heat exchanger from the stop valve through a process water pump at an inlet pressure of 0.8MPa; and the process water after heat exchanger enters a diluted steam system through the stop valve at a pressure of 0.56-0.6MPa. The process design is reasonable, the probability of the quenching oil entering the process water is obviously reduced, the heat exchange effect of the heat exchanger is improved, the process water system operates normally, the operation cycle of the device is prolonged, and * million yuan is created for a factory each year.