This paper presents computational fluid dynamic (CFD) analysis of a natural draft top-lit up-draft (TLUD) biomass cookstove which is acting as a micro pyrolyzing reactor to produce biochar. The effect of the top end geometry, the number of primary and secondary air inlets and their hole patterns, and the number of secondary air outlets and their hole patterns were considered in the design to optimize the performance. Seven different cookstove geometries were simulated to analyse the temperature and air distribution. ANSYS Fluent 16.0 was used to simulate the simplified 3D computational domains of the cookstove designs. The design with uniform air distribution and proper mixing of secondary air and the producer gas was selected as the best cookstove design to fabricate. Experiments were performed with the selected design and the results were compared with the predicted simulation results for evaluating the model. Results revealed a good correlation of 96.67% and a higher R 2 (coefficient of determination) value of 0.9344 for the temperature inside the combustion chamber. Thus, this modelling methodology can be used for the optimization of existing biomass cookstoves and for evaluating naval cookstove designs.