Common methods of furoxan ring formation were analyzed. Main preparation reactions of cyanide oxide and their advantages and disadvantages were summarized, such as the reaction of hydroxamic chloride and weak base,the reaction of aldehyde oxime and nitric oxide, the reaction of hydrazide potassium salt and oxidants, et al. Dimerization reaction of cyanide oxide leads to formation the furoxan derivatives with symmetrical substituent groups. The properties of some symmetrical furoxan derivatives were listed.