Three types of vegetable oil, transgenic rapeseed oil, transgenic peanut oil and cotton-seed oil, are used as raw materials in experiments to obtain the refined insulating oil. The dosage of reagent in experiments is studied for vegetable insulating oil refinement. Furthermore, basic physical and chemical properties of the three types of vegetable insulating oil are analyzed. The electrical properties including breakdown voltage, dissipation factor, dielectric constant, and volume resistance are studied and presented. By compared with each item of properties of the three types of vegetable insulating oil, rapeseed-oil-based insulating oil is considered to possess the best properties due to the fact that it is more abundant of mono-unsaturated fatty acid than the other two types of insulating oil.