The invention relates to a main steam temperature PID (Proportion Integration Differentiation) control method of an ultra supercritical unit for boiler power generation in a thermal power plant based on an improved genetic algorithm. The method comprises the improved genetic algorithm. The improved genetic algorithm is improved on the basis of a simple genetic algorithm, optimal sequencing retaining selection, non-uniform linear intersection and Gauss mutation operators are introduced, a uniform design method is adopted to construct an initial population, and the intersection and variation probability is adjusted by Sigmoid function adaptability; and a PID controller orienting a DCS (distributed control system) is adopted, and the parameter set of the controller under a part load section is optimally obtained through the improved genetic algorithm. The optimizing speed and precision of the genetic algorithm are improved, the control method can replace an engineering adjusting method with complex engineering and low accuracy, the workload of on-site debugging personnel is reduced, the purpose of intelligent main steam temperature control is achieved, the application of an intelligent optimization technology under the DCS is realized, and the need of stably controlling the main steam temperature of the ultra supercritical unit in deep peak regulation is met.