Nowadays, when designing screw compressors, it is often necessary to promptly determine future characteristics, such as delivery ratio, efficiency, etc. These features are highly dependent on clearances between the working elements of compressors, which change as a result of thermal deformation of rotors and casings. At the moment, there are two ways to account for thermal deformations. Firstly, the evaluation of the average temperature pattern by approximation dependence built on experimental data, with further evaluation of deformation according to the law of linear expansion. This method is fast and low-cost, but it can have a large error both as a consequence of a significant deviation of the evaluation mode from the modes in the experiment to determine the dependence of the temperature pattern and as a consequence of applying a simple linear formula for deformation evaluation for rotors with a complex shape. Secondly, evaluation of temperature distribution based on the finite difference method, taking into account the specific conditions of heat exchange in the evaluation mode, and further evaluation of rotor deformation taking into account the complex shape by the finite difference method. This method has higher accuracy and flexibility but is very labor-intensive, time-consuming and requires setting precise initial conditions. This paper compares results of the screw compressor rotors’ thermal deformation calculation obtained by using both methods, and considers the possibility of applying the method for evaluation of rotor deformation that combines the positive aspects of both approaches.