This paper discusses numerical simulation and experimental studies of different operating conditions of biomass gasification on the performance of an updraft gasifier high temperature air gasification (HTAG). The influence of gasification temperature and equivalence ratio (ER) on gas production and tar yield were examined. A mathematical model was used to simulate the effects of the parameters that influence the process of gasification. The results indicated that H₂ and CO contents and low calorific value gas production rate increased. Additionally, there was a decrease in tar yields, CO₂ content, and the temperature of the gas products necessary to reduce the CH₄. The present study proved that ER significantly influenced the composition of gas species products and helped obtain a higher gasification rate. The results showed that the model proposed in this study is a promising tool for simulating the gasification/combustion process of biomass within a gasifier.