The temperature fields of multiple cross sections along the axis were measured under steady condition on the engine test bench by revolving the in-line distributed thermocouples in SCR catalyst container and the influence of ammonia-nitrogen ratio (A/N ratio) on the temperature field distribution of SCR catalytic container was studied. The results show that the uniformity of temperature distribution deteriorates with the increase of A/N ratio at A/N ratio of less than 1. When A/N ratio is beyond 1, the increase of A/N ratio has little influence on the temperature distribution at low exhaust temperature, but the uniformity of temperature distribution becomes worse with the increase of A/N ratio at high exhaust temperature. With the increase of A/N ratio, the average temperature of SCR entrance section decreases, the average temperature of each cross section in the catalyst gradually increases because the heat release of reaction is greater than the heat loss and the catalyst temperature of the rear end is higher than that of the front end.