In order to further explore the influence of hydrochloric acid pretreatment on the pyrolysis characteristics of biomass, the thermogravimetric method was used to compare and analyze the pyrolysis characteristics of corn straw and poplar before and after pickling under low heating rates (10℃/min, 20℃/min, 30℃/min, 40℃/min and 50℃/min). The kinetic parameters and corresponding thermodynamic parameters of pyrolysis process were calculated by distributed activation energy model (DAEM), and Fourier transform infrared spectrometer (FTIR) was used to analyze the change of chemical structure of biomass before and after pickling. The results showed that the pyrolysis process of biomass experienced four stages：water loss (room temperature~120℃), glass transition (120~210℃), main pyrolysis (210~400℃) and carbonization (400~700℃). Pickling pretreatment increased the maximum weightlessness rate and the final weight loss rate of biomass pyrolysis, and reduced the generation of coke. Under the conversion rate of 20%~70%, it was calculated that the pyrolysis activation energy of corn straw and poplar before and after pickling were 218.27~340.08kJ/mol,  225.17~291.73kJ/mol, 227.35~254.76kJ/mol and 197.39~235.52kJ/mol，respectively. At the same time, the ΔH of corn straw and poplar before and after pickling were 29109~291.28kJ/mol, 249.68~249.82kJ/mol, 228.68~228.86kJ/mol and 221.78~221.93kJ/mol, respectively. The ΔG were 119.23~122.92kJ/mol, 118.57~125.09kJ/mol, 123.78~128.22kJ/mol and 121.97~129.29kJ/mol, respectively. The ΔS were 26654~271.42J/(mol·K), 198.01~206.29J/(mol·K), 156.53~159.14J/(mol·K) and 144.02~153.81J/(mol·K), respectively, indicating that hydrochloric acid pickling pretreatment on the whole reduced the activation energy, enthalpy change and entropy change in the process of biomass pyrolysis, increased the Gibbs free energy (ΔG), promoted the pyrolysis reaction. The infrared spectrogram of the corn straw and poplar were similar before and after pickling, but there was a significant intensity change at the same absorption peak, indicating that the pickling pretreatment had different influence on the organic functional groups of different biomass. The research result can provide theoretical basis for the efficient utilization of biomass and the design of pyrolysis process parameters.