Abstract: Cottonseed oils as base ingredient,soybean oil,colza oil and palm oil were added to obtain a blend oil for frying by different compound proportions. The quality of frying oil was investigated by checking the changes of color,physical and chemical,safety and health indexes in the continuous frying experiments. The results showed that the blend oil had a reasonable fatty acid composition with the optimal intake ratio of monounsaturated fatty acids/polyunsaturated fatty acids of 4.0:0.6. The frying process of the blend oil,which was slowly color-changing,sustained 67 h until the contents of polar compounds more than 27%,the acid value increased from(0.18±0.05) mg/g to(3.53±0.10) mg/g,carbonyl value raised from(9.42±0.12) meq/kg to(36.0±0.14) meq/kg,peroxide and benzopyrene values had no clear trend,and acrylamide was not detected. Compared to grade 3 cottonseed oil which usually had high carbonyl,peroxide and benzopyrene values in 46 h frying process used in Hebei region,the frying time of the blend oil extended 18 h during frying process,frying quality stability increased 37%,and the average oil contents of fried French fries was 18% had the good sensory effect which could be used as a specialized blend oil for frying.