This study evaluates the biomass-to-synthetic natural gas (SNG) using calcium looping gasification (CLG) with CaO sorbent (CLG-SNG) via thermochemical methods. The CLG-SNG process consists of three steps in sequence: steam gasification in situ CO2 capture using CaO sorbents, gas cleaning, and methanation. The concept of interconnected fluidized beds was adopted for repeated carbonation/calcination cycles of CaO sorbents in the gasification unit. A process simulation was conducted based on the chemical equilibrium method using Aspen Plus. Then, the effects of some key variables on the thermodynamic performances, such as the gas composition, yield of SNG (Y-SNG), cold gas efficiency (eta(cold)), the overall energy efficiency (eta), exergy efficiency (psi) of the process, and the unit power consumption (W-SNG) were investigated. The variables include CaO-to-biomass ratio (Ca/B) in the range of 0.7-1, steam-to-biomass ratio (S/B) in the range of 0.1-1.5, and gasification temperature (t(G)) in the range of 600-700 degrees C. At Ca/B = 0.83, i.e., a stoichiometric number of SN = 1, the CH4 content in SNG and W-SNG each reach the maximum while the Y-SNG reaches the minimum. With S/B increasing from 0.1 to 1.5, CH4 content in SNG gradually decreases while W-SNG shows an increasing tendency. Y-SNG, eta(cold), eta and psi reach the maximum at S/B = 0.6 (i.e., when the gasifier reach the heat equilibrium). Generally, lower tG values are favorable for the thermodynamic performances (mainly Y-SNG and eta(cold)) of the CLG-SNG process. The optimal performances demonstrate that the CLG-SNG process has a strong competitiveness, compared to the traditional SNG production process.