Industrialization and growing environmental concern are increasingly leading to the search for energy sources that emit less greenhouse gases. Biomass, due to its great accessibility around the world and its diversity, is a strong alternative to fossil fuels. Its gasification produces a gaseous fuel called syngas. The urban solid waste (MSW) management problems and the wide availability of sugarcane bagasse in Brazil made them types of biomass of interest for this work. This work aimed to model biomass gasification in MATLAB ® for a downdraft gasifier and air as gasifying agent, using a kinetic approach. The model was validated with experimental and numerical data from the literature and was then applied to MSW and sugarcane bagasse co-gasification simulation, in which co-gasification ratio (CGR) represented MSW percentage in the incoming biomass. A central composite design of experiments with 3 factors and 3 levels was carried out, resulting in 27 tests varying CGR, biomass moisture and equivalence ratio. Polynomial models were created for syngas composition, syngas LHV, process energy efficiency and sum of CO and H2 molar fractions on a wet basis. The models were considered robust, with values of R2 and adjusted R2 ranging from 0,96082 to 0,99345 and 0,94007 to 0,98998, respectively. The impact of each chosen factor was investigated, and the energy efficiency and sum of CO and H2 molar fractions models were maximized. The optimized case, with CGR 7,98 percent, biomass moisture 5,00 percent and equivalence ratio 0,18, resulted in a syngas composition of 3,72 percent H2O, 29,68 percent CO, 7,87 percent CO2, 19,07 percent H2 and 0,80 percent CH4 in molar basis, corresponding to a LHV of 6,56 MJ/Nm3 and an energy efficiency of 37,66 percent. By the end, the process showed great potential to produce a syngas rich in CO and H2.