Diesel generator set is an ideal choice for backup power supply of sluice project because of its fast start-up,smooth operation and simple operation.In order to meet the requirements of economy,energy saving,safety and reliability，it is very important to select the capacity of diesel generating set reasonably.This paper analyses the clauses and explanations of the diesel generating units in the relevant codes.In view of the sluice project，the matters needing attention in the application of the formula for calculating the capacity selection of diesel generating units are put forward，and the steps for capacity selection are given as the reference for engineers.