Flatness and parallelism which have relations and differences between them are two important subjects in shape-position tolerance theory. It is necessary to be discussed in detail through analysis, research, comparing and summarizing as they are widely used in industry whereas their concepts are easily be confused. This paper carries on the comparison based on the following aspects. (1) Definitions of tolerance zone. (2) Tolerance category, Marking methods and tolerance values. (3) Measuring methods. (4) Examples. For a object with given flatness and parallelism tolerance, the similarities and differences are analyzed and compared in the views of shape,size,direction and position etc. It would be useful references to personals in engineering, technology and other relevant fields.© (2010) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.