The eastern Himalayan syntaxis is the key geological region to understand the tectonic evolution of the Qinghai- Tibet Plateau where major engineering projects such as the Sichuan- Tibet railway and hydropower stations in the lower Yarlung Tsangpo River have been planned. However, the current in- situ stress field of this region is still unclear yet due to the complex geological and geographical conditions. Based on in- situ stress data that were obtained recently using the hydraulic fracturing method in this region, the current in- situ stress filed of the Tongmai- Bomi section, which is located in the northern margin of the eastern Himalayan syntaxis, is determined in detail. Furthermore, the current tectonic stress environment is estimated and discussed by adopting the Coulomb frictional- failure criterion and Byerlees law. The results indicate that the measured principal stresses SH and Sh show increase pattern versus depths and range 4.87~32.47 MPa, and 3.05~20.07 MPa within 1000 m depth below surface, respectively. The increase gradient coefficients of S H and Sh versus depths are 2.49 MPa/100 m, and 1.61 MPa/100 m, respectively, being lower than the corresponding gradient levels of the Qinghai- Tibet block and the western margin region of the eastern Himalayan syntaxis. However, the characteristic parameters representing the in- situ stress state reveal that the horizontal stress intensity in this region is greater than that of the Qinghai- Tibet block. The orientation of SH of the Tongmai- Bomi section derived from hydraulic fracturing tests is dominantly in NEE direction, with a mathematical average magnitude N69.2°±11.5°E, showing a clockwise deflection pattern comparing with the dominant NNE- NE regional tectonic stress direction derived from other tectonic stress indicators. The measured in- situ stress data reveal that the horizontal stresses play a dominant role in the generation of the current in- situ stress field, and the stress regime is considered to be thrust faulting within depths shallower than 400 m, and strike- slip faulting under 400 m depth below surface. The values of horizontal differential stress and tectonic differential stress increase significantly under 600 m depth below surface and the latter can reach up to 12.42 MPa, indicating that there is relatively high regional tectonic stress in the Tongmai- Bomi region. Estimation of the in- situ stress field using the Coulomb frictional- failure criterion incorporating the Byerlees law indicates that the value of measured in- situ stress below 200 m depth which may not be affected by the topography is generally lower than the theoretical limit calculated by assuming friction coefficient to be 0. 6. In addition, the patterns that measured in- situ stress below 430 m depth distribute within the theoretical range calculated by assuming the friction coefficient to 0.2~0.4 leads to an insight that the current in- situ stress level of the Tongmai- Bomi section does not exceed the lower limit of the upper crust controlled by the frictional strength of faults. Collectively, it can be noted that the Tongmai- Bomi region is in the relatively stable tectonic stress environment. Finally, the influence of the current in- situ stress condition on the planned major railway tunnels is discussed and corresponding suggestions are put forward.