The invention discloses a main line green wave coordination control signal time method for optimizing exhaust gas emission. The method comprises the following steps that first, the basic traffic parameter of a main line is surveyed and obtained, and a vehicle exhaust gas emission calculating platform is initialized; second, the basic parameter of a multi-objective genetic method is set, and a population of the multi-objective genetic method is initialized; third, based on the platform, the adaptive degrees of all individuals in the population are calculated; fourth, the non-domination sequence and the visual adaptive degree of the individuals in the population are calculated, a progeny population is generated through genetic section, genetic cross and genetic variation, and the adaptive degrees of all individuals of the progeny population are calculated; fifth, the population and the progeny population are combined to obtain a new population, the non-domination sequence and the congestion degree of all individuals of the new population are calculated, the individuals are chosen based on the non-domination sequence and the congestion degree, and the next generation population is obtained; six, when evolution algebra is larger than the best evolution algebra, execution of the method is completed, all the individuals with the non-domination sequence being equal to 1 in the last generation population are used as a final noninferior solution to be output, and the timing scheme in which the vehicle average delay and vehicle exhaust gas emission are comprehensively considered is obtained.