The invention relates to an optimization type selection method, a sample database and a system of fans in sewage treatment plant design. The method includes step1 calculating air supply quantity and required pressure in the largest flow time section, the average flow time section and the smaller flow time section of an activated sludge system, step2 selecting type selection accuracy of the fans and maximum number of working platforms; step3 preferably selecting fan types meeting design requirements of the three flow time sections and the number and the running state of the working platforms in each time section; step4 returning to execute the step2 and reducing the type selection accuracy of the fans or determining the maximum number of the working platforms again if fans meeting the type accuracy requirement cannot be selected; and step5 queuing the fans according to energy consumption if the types of the selected fans are larger than 1 and providing the most energy-saving fan and a running combination of the fan for a user to achieve the aims of saving energy and improving working efficiency.