Effects of microwave, far-infrared heating and hot-air treatment on enzyme activity of walnut kernels were investigated. After undergoing different strength of microwave, far-infrared ray and hot-air, the activity of lipoxygenase activity (LOX), peroxidase (POD) and hydrogenperoxidase (CAT) in walnut kernels were determined. The results showed that microwave, far-infrared heating and hot-air treatment could inhibit the activity of LOX, POD and CAT effectively. The conditions of three heat processing were optimized as follows, i.e. treated at 385 W microwave for 3 min, 90 ℃ far-infrared heating for 30 min, or 90 ℃ hot-air treatment for 90 min, respectively.