Abstract: In this paper, the method how to use the results of land grading and evaluation to estimate the price of lot by combining the Market data approach with the system of land grading and evaluation is discussed. Market data approach is one of the most important methods of land evaluating. It conform s to the rules of substitution and analogy. Traditional process of Market data approach is realized by gathering data artificially, estimating the degree of analogy by expert experience. The influence of all factors to be modified is decided by ex pert. Because of the lack of the standard of quantity, the result of estimating is greatly controlled by person's subjectivity. In the Market data approach based on land grading and evaluation, region factors used in land grading and the factors used to modify lot price are selected by experts. Experts also give the power of region factors. According to the rules of land grading, the methods of calculating index of region factors' condition are established. Combining the statistic of land's marketing exchange material with experience of experts the modify ing system of lot's price is formed. The problem that structure of database used in the process of lot evaluation is dynamic and is designed by template and relevant dada structure. By the use of mathematics method such as analysis of classification, the data structure and algorithm of matching and collecting evaluated lot instance automatically and evaluating price of lot evaluated automatically are designed. The functions of Market data approach are realized in land grading and evaluation information system based on GIS. It overcomes the shortcomings of traditional process of Market data approach. So the results will be more scientific, objective and reasonable.