Abstract: With the popularity of BIM technology and its application, project review and approval based on the trend that BIM has increasingly developed, instead of 2D drawing. BIM checking from model information data to checking data usually needs to apply kinds of algorithms. Based on Revit platform and RevitAPI, this paper studied the application of convex hull algorithm in the calculation of building contour. According to the convex hull algorithm, this paper proposed a general algorithm called concave envelope algorithm on the basis of MultiLineString data and explored the application of concave envelope algorithm in the calculation of building contour line. Depending on the common modeling methods of building models, this paper further presented a more suitable method for calculating the building contour with room information. Comparing the three calculation methods, a more suitable algorithm for building contour calculation was given in paper.