Physicochemical characteristics of wood powder acid hydrolysis residue (WAHR) were studied firstly in this study, and WAHL (lignin derived from WAHR) was separated successfully from WAHR based on an improved isolating method. The content of functional group such as phenolic hydroxyl group of guaiacyl, syringyl, and hydroxyl-phenyl units in WAHL were identified by P-31-NMR and DFRC (derivatization followed by reductive cleavage) method. Thermal degradation experiments were carried out on a thermogravimetric (TG) analyzer to show pyrolysis characteristics of WAHL. The compositions of pyrolysis products of WAHL were also studied throughout a pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) analyzer. It was shown that the pyrolysis of WAHL took place in a wide temperature range and there were two obvious peaks in the differential thermogravimetric diagram. Results of Py-GC-MS analysis indicated that pyrolysis products were mainly formed through cleavage of the beta-O-4 connection and multiple pyrolysis.