To make agricultural marketing policies be carried out more easily, this research establishes a decision support system by using the rice field of one farmer in Changhwa area, Taiwan as the example and explains how this decision support system works. Actually, this research has three purposes: 1.To study how key production factors affect the yield of rice variety No.67. 2.To establish a decision support system to forecast the yield of rice variety No.67. 3.To use Visual Basic to write computer programs which can simulate how yield changes if key production factors change. There are four sections in this paper: literature review, the establishment of decision support system, example and conclusion.