The thermal behaviour of unidirectional continuous carbon fibre reinforced composites has been studied using micromechanical FEA methods. The micromechanical analysis has been focused on three primaries. First, two linear FEA models are developed in Abaqus software to represent two typical fibre arrangements in unidirectional composite materials (Square and Hexagonal). The linear models are verified by comparing the effective transverse and longitudinal CTE (Coefficient of Thermal Expansion) with predicted data from several available explicit equations. The modelling results are in good agreements with the theoretical predictions, especially with Schapery equation. A sensitivity analysis was also conducted to determine the influences of constituent properties on the longitudinal and transverse CTE.The second part of the dissertation is focused on the thermally induced deformations and stresses for the unidirectional M40J/HTM556 lamina using nonlinear micromechanical analysis. The nonlinear FEA models are developed based on the linear model by considering the temperature dependency of constituent properties (especially the Young's modulus, Poisson's ratio, CTE of resin matrix), the effect of stiffen interphase and thermal residual stress developed during cure process. Two types of thermal expansion coefficient (Overall and Average) are defined and used to compare the numerical results with the experimental results from TMA and Strain Gauges techniques. A good agreement is shown between numerical and experimental results for transverse CTEs. The prediction of longitudinal CTE is in relatively poor agreement with the experimental results. The reason is also analyzed and considered to result from experimental errors. Finally, the thermally induced stresses within carbon fibre and resin matrix are also predicted from the nonlinear micromechanical analysis. It is found that the thermal stress within resin matrix at -60oC is more than 80MPa, which is considered to be big enough to introduce micro-cracks in the matrix.