Pyrolytic behavior of pubescens samples pretreated by 0, 5, 10, 15, and 20 wt % MgCl2 solution and HCl solution (with the same pH value as 5 wt % MgCl2 solution, namely, pH 5.11) at room temperature was studied. The feedstock and pretreated samples were analyzed by thermogravimetric analysis, and the bio-oil was analyzed by gas chromatography-mass spectrometry, gas chromatography-flame ionization detector, high-performance liquid chromatography, gel permeation chromatography, electrospray ionization mass spectrometry, and two-dimensional heteronuclear single quantum coherence nuclear magnetic resonance (2D HSQC NMR). The pretreatment of MgCl2 raised the yield of furfural from 0.27 to 2.61 wt % caused by the promotion of 20 wt % MgCl2 solution on the dehydration reaction of hemicellulose, while the yields of phenols, formic acid, and acetic acid were reduced. For the distribution of oligomers in the bio-oil, the content of species with M-n = 260-500 Da increased, whereas that of the species with M-n > 500 Da decreased significantly. Meanwhile, the contents of phenolic oligomers decreased, while the contents of hemicellulose-derived oligomers increased, which could be attributed to the promotion of MgCl2 on the depolymerization of hemicellulose. A new species composed of cellulose and hemicellulose moieties, namely, X-MeGlcA(4), appeared in the 2D HSQC NMR spectra of the bio-oil, which could be related to the co-degradation of cellulose and hemicellulose.