The invention belongs to the field of building project modeling software research and development and application, and particularly relates to a design drawing splitting method and system based on a .NET plug-in, and the method comprises the following steps: 1, formulating a drawing splitting rule; 2, acquiring a preset layer set; step 3, circulating the image layer set to obtain a multi-line-segment set; 4, acquiring rectangular coordinate points of the multi-line layer; 5, splitting the drawing file; and 6, storing the split file in a fixed format according to the rule and uploading the split file to a design drawing management system. The design drawing splitting system based on the. NET plug-in comprises a drawing uploading plug-in, a drawing splitting monitoring service plug-in and adrawing splitting plug-in. The method and system solve a series of problems that design drawings with different geometric figure calculation resource consumption and different design habits are difficult to draw, the design drawing utilization rate is poor, drawing sharing is difficult, an existing design drawing plug-in splitting algorithm is complex and long in time consumption, and the requirement for computer equipment performance is high.