Based on wavelet transformation by different decomposing levels,the near-infrared spectroscopy signals of 138 intact zanthoxylum bungeagum maxim samples were denoised and some PLS-LOO-CV(partial least squared-leave one out-cross validation) operations were proposed for the prediction of volatile oil content with the reconstructed spectra after denoising.The results were not the same when the wavelet decomposing level was different.The PLS-CV result was the best at a wavelet decomposing level of 4.The determ...