The aim of this paper is to find out the factors of price volatility and illustrate the chain of process where the wholesale price of green onion fluctuates at an interval of three to four months. In order to achieve this objective, we designed a econometric model. We discovered that according to our estimation, the wholesale price of green onion is affected by production amount rather than the amount of shipment made into the market. Price instability becomes more acute especially when the amount of green onion shipped to the market is larger than the annual average during when two cropping methods overlap. In order to reduce the periodic fluctuation of the wholesale price, we suggested that it is necessary to develop a monitoring system that can provide information about the production and supply and demand before a producer selects the cropping land for next harvest.