The invention discloses a citrus vein phloem degeneration diagnosing method based on parameters collected by MINI-PAM. The method comprises the steps that firstly, various fluorescence parameters of citrus leaves are collected through the MINI-PAM and sent to a computer; secondly, the computer carries out strange sample removing and primary processing on the original data collected by the MINI-PAM; thirdly, a probability neural network sub-classifier is established and used for carrying out classifying training on various disease type data of the citrus to obtain a citrus disease classification model; fourthly, the various sample fluorescence parameter data collected by the MINI-PAM are input to the disease classification model to be classified; fifthly, the probability algorithm is executed according to the classification output result of the disease classification model to obtain corresponding judgment probabilities of various disease types, and whether the citrus gets the vein phloem degeneration or not is determined according to the probability result. The citrus vein phloem degeneration diagnosing method has the advantages of being fast, accurate and free of destructiveness.