Using the Sliding Direction Fitting Method to invert the fault slip data measured on the critical tectonic position of the main active faults in the middle-eastern part of northern Tienshan Mountains，we got 17 tectonic stress tensors and obtained the basic characteristics of tectonic stress field in the research area． The inverted result shows that the recent tectonic stress field in middle-eastern part of northern Tienshan Mountains is characterized by near N-S maximum compressional stress，and the stress regime is mainly of reverse slip，with some cases of strike slip． This result inverted from fault slip data is greatly matched with that obtained from focal mechanism solutions in this region and it indicates that the tectonic stress action has good stability in a long geological period time．