Under free economic system, the market transaction activities are able to occur only in the supply and demand of buyer and seller. The supply and demand are composed of law of supply and demand that is market mechanism, while law of supply and demand is the important factor of market economic activity. The change of market demand includes the change in the quantity demanded and the change in demand. This research aims to study the influence of place marketing on law of supply and demand in the change of market demand and price. The case study uses regressive forecasting and Grey forecasting separately. Through average price forecasting of bluefin tuna in Tong Kang, this research studies the influence of bluefin tuna tourism season, held by Pingtung County government, on bluefin tuna sale. The result of this research be proved there have some influence of place marketing on market mechanism in the change of market demand and price.