Based on the first law of thermodynamics and the second law of thermodynamics,the exhaust energy of diesel engine was calculated and analysed. With the round speed and torque increased,the exhaust energy increased generally. At the condition of peak power,the max value of exhaust energy was 176. 40 k W,and at the condition of peak torque the value was 144. 80 k W. Also the exergy of the exhaust energy was increased with the round speed and torque increased. The max value of exergy was 74. 19 k W at the condition of peak power and the value of exergy was 61. 46 k W when it was at the condition of peak torque. In theory,the thermal efficiency was increased by 6. 8%-11. 5% when the exergy of the exhaust energy was fully used.