Abstract: With extensive development of tolerance simulation analysis in agricultural machinery industry, tolerance simulation analysis technology is more and more applied in grain harvester．Three types of tolerance simulation analysis, namely extreme method, probability method（one-dimensional tolerance simulation analysis method）, and Monte Carlo method（three-dimensional tolerance simulation analysis method）, were used to analyze and calculate dimensional technical specification（DTS）requirements in door system．Effectiveness and rationality of each tolerance analysis method were verified by measuring dimensions of physical sample harveater．Results showed that Monte carlo method was basically consistent with actual assembly effect, and it provided a more reasonable analysis method and solution for assembly problem．At the same time, it could scientifically guide dimension tolerance design of door system of grain harvester．