For the NOx concentration at the inlet of denitration reactor for coal-fired boiler, an important parameter in the combustion process for the boiler, the precision of conventional NOx analyzer is low. Therefore, a NOx emission prediction model for the boiler was established based on the support vector regression (SVR) algorithm, with mean square error (MSE) as the evaluation function for the model. The genetic algorithm (GA) was adopted to optimize relevant parameters of the model, and the NOx emission was predicted through programming. A simulation verification was carried out based on the field data of a 300MW coal-fired unit, and the results showed that the model established by GA-SVR was more effective than SVR and BPNN in the NOx emission prediction.