The invention belongs to the technical field of determining of tobacco field harvest maturity and harvest period, and relates to a method for determining the one-time harvest maturity of 5-6 tobacco leaves at the upper part of a tobacco by measuring the chlorophyll content (SPAD value) of the first, third, fifth or sixth leaves counted from up down of the tobacco. According to the method, 20 tobaccos are randomly selected from tobaccos of each mu planted, the first leaf, a chlorophyll measurement instrument is used for measuring the average of the contents of the first leaf, the third leaf, the fifth leaf or the sixth leaf at the upper of tobacco respectively, the measured average value is used as the maturity index complying with one-time harvest when the average value is 20-30 and the chlorophyll contents of the first leaf, the third leaf, the fifth leaf or the sixth leaf have no obvious difference, harvesting tobacco in fields can be carried out. The measuring method of the invention has definite index, has impersonal judgment index, and is easy to operate and master, and tobaccos harvested by using the method have good tobacco maturity and higher quality.