Abstract: The marginal utility of average commodity degreases with the increase of this commodity,so does its exchange value,for the entity of the exchange value is the value in use,in other words,the marginal utility of commodity.The more the commodities are,the more people need and desire for,and so the unsatisfied needs and desires become fewer and less important,finally leading to the least important needs and desires caused by average increase,least marginal utility,least value in use,least entity of exchange value,and least exchange value of average commodity.

Key words: exchange value, entity of exchange value, value in use, marginal utility