Abstract: Through the analysis of hot rolling processes by establishing a vaporizing combustion zone, it was found that the oil-water mixture kept liquid and there was not enough time to reach its burning point both in the entry vaporizing combustion zone and deformation zone. Oil film strength tests, friction coefficient tests and long grinding experiments were carried out on a four-ball machine. Wear scars showed that when the mass concentration of the rolling oil in water was more than 2 g·L^-1, the lubrication regime was boundary lubrication, in which the lubrication effects depended on the strength of oil films, not oil concentration. Rolling lubrication in production with an oil mass concentration of 2 g·L^-1 was tested; it proved the above-mentioned research results. The rolling force was effectively decreased and the cooling water pollution was minimal at the same time. It was recommended that the mass concentration of the rolling oil should be less than 10 g·L^-1 for different rolling products and processes; otherwise the rolling oil residues might cause the cooling water polluted.