The invention discloses a method for detecting the thickness of a tobacco leaf. The steps are that first, conducting sampling process; second, collecting optical spectrum; third, building a mold, and fourth, detecting and obtaining the thickness value of a sample by ingeniously using a tobacco powder calibration model which is built in the third step and a near-infrared spectrogram by scanning unknown sample tobacco powder in the second step. The method is simple in preliminary treatment, collecting of the optical spectrum of one sample can be completed only in one to two minutes, calculating average spectrum is of no need, collecting time is short, analyzing speed is fast, the data of a to-be-detected sample can be directly given by invocating the module, so that the collecting time of the optical spectrum is greatly saved, the amount of labor is reduced, the speed of building the module is raised, low mean square residual is obtained by the calibration module, the effect of building the module is good, and detecting speed is fast.