Abstarct: Nowadays, underground coal gasification (UCG) method is going to consider as a suitable alternative for traditional thermal coal mining methods. This method involves the injection of steam and air or oxygen into an underground coal seam and igniting and burning of coal in-situ to produce the combustible gas. During underground coal gasification (UCG), whereby coal is converted to syngas in-situ, a panel (cavity) is formed in the coal seam. The Controlled Retraction Injection Point (CRIP) configuration in the form of two and three panel is widely used in commercial scale. Unlike other underground mining methods, the coal and country rocks in the vicinity of a UCG panel are subjected to the high temperatures which may be in exceed to of 1000 °C. UCG operation imposes significant geomechanical changes to the strata. In order to understand these changes, the numerical modeling can provide a comprehensive and qualitative understanding of UCG process. The aim of this research is to determine panels dimensions in UCG baxsed on CRIP configuration with the use of thermo-mechanical modeling. For this purpose, at the first, a non-linear multivariable empirical model developed to predict cavity growth rate and panel width. In addition another empirical model is developed to estimate protection pillar width baxsed on the CRIP configuration in UCG. The UCG process involves complex chemical, thermal, hydrological and mechanical processes. Therefore, the complex interactions among these processes make it challenging to understand UCG process. Furthermore, since the UCG process takes place in underground it is difficult to use instruments to monitor the entire coal reaction conditions, stresses distribution, caving behavior and its effect on the surrounding rocks. In order to preserve the gasification process in normal conditions, it is necessary to know the roof displacement, stress distribution in the vicinity of the gasification panels. Thus, numerical modeling of the UCG process may provide an alternative to achieve a comprehensive and qualitative understanding of such a complex process. Secondly, a new methodology for 3D Thermal-Mechanical (TM) model is developed for UCG baxsed on CRIP configuration to estimate suitable UCG panel dimensions using the FLAC3D software. For this purpose a new algorithm is developed for CRIP method in which two panels and protection pillar between them are considered. In numerical model, gasification has been started at the first panel and then continued to the second panel. In numerical modelling, a panel is subjected to high syngas pressure and high temperature. Moreover, after each step of gasification the modeling of caved material has been performed. Finally, this methodology is used to estimate suitable UCG panel dimensions in 3.5 m M2 coal seam thickness in Mazino coal deposit. The results of side abutment stresses show that 150 m panel width and 42 m pillar width is suitable for design of UCG panel in M2 coal seam at the depth of 600 m.