The additional lateral tooth was installed on the vertical tooth of the staggered seals to improve seal efficiency and reduce vibration,and a new kind of mixed seal was put forward.The three dimensional computational fluid dynamic (CFD) calculation model was set up.Analysis and comparison between the two kinds of seal were done at different working conditions.Results show that the leakage of the newly designed compound seal is about 70 percent of that of the staggered seal because the compound seal,which installed additional lateral tooth on the vertical tooth of the staggered seal,can reduce leakage ratio in axial/radial direction.Both of the radial and the tangential force of the compound seal are smaller than that of the traditional staggered seal.The advantages of the compound seal are more distinct in improving seal efficiency and reducing vibration in the cases of high pressure ratio,high rotating speed and high pre-swirl speed.There is large influence of the lateral tooth length on the tangential force of the compound seal.With the length of the lateral tooth increases,the tangential force drops and rotor becomes more stable.The lateral tooth length should be as long as possible on the premise of that it meets the demand of axial expansion of the turbogenerator unit during running down and running up process.