Abstract: The effects of different isothermal aging parameters on thermal expansion curves and microstructure of Q235/304L contact were studied, and Q235/304L contact state under different temperature control conditions at near zero pressure was analyzed. Q235/304L contact state under different temperature control conditions at near zero pressure was anglyzed. Effect of isothermal aging on thermal expansion of Q235/304L contact was studied by quenching dilatometer and metallographic microscope. The results show that, when the heat preservation temperature is above 1000 ℃, the thermal expansion curve can reflect the characteristics of the contact state of steel species. The isothermal aging treatment with temperature of 1100 ℃above and holding time of 5 h is beneficial to Q235/304L close contact.