Abstract: The TN-Ⅲ inner pipe cementing device was developed to prevent seal part from failure and improve secure reliability of operation and cement quality, in the light of the existing problems of original bottom hole sealed inner pipe cementing device. The device can move the seal part from the bottom hole to the wellhead. It can be applied in well cementing with various large diameter casings. The TN-III inner pipe was patented nationally(Patent Number:95213958. 8) and used in 3 wells with good results.