Exhaust manifold is a main heated component of engine,which has poor working conditions. High levels of thermal load can lead to deformation even cracking,which affect its normal working and reliability and durability. Aiming at the high thermal load of a high pressure common rail diesel engine,different fluid-solid coupling models was built and the temperature distribution and thermal stress of the engine exhaust manifold was stimulated and the influence of different structural factors on the exhaust manifold thermal load was calculated and analyzed. Results show that: the maximum temperature of the exhaust manifold changed from 805. 2 ℃ to 820. 8 ℃ as the outlet length increased,the maximum temperature of the exhaust manifold changed from 805. 2 ℃ to 819. 4 ℃ as the outlet diameter increasing,and the maximum temperature of the exhaust manifold dropped to 784. 0 ℃ as the outlet transferred to the body symmetry position. Structure factors such as exhaust outlet position,outlet length and outlet diameter had a great influence on the exhaust manifold thermal load. The maximum thermal stress value was 326. 21 MPa of the case of 21 mm outlet length and 5 mm outlet diameter outlet with the non-symmetry outlet position; the minimum thermal stress value was 174. 1 MPa of the case of 19 mm outlet length and 5mm outlet diameter with the non-symmetry outlet position.