The goal of this work is in twofold: 1) to determine the directional deformation (deflection) and bending stress of 1.25 MW Suzlon wind turbine tower under loading conditions for different cross-sections through finite element analysis method; 2) to develop and validate the analytical model allowing to estimate same for different cross-sections. Wind shear force has been calculated in the prevailing direction of the wind for tower structures through integral equations, are then used as input for 3-dimensional finite element model to compute the tower deflection and bending stress. To improve the estimation of tower deflection, a mathematical model is developed based on cantilever beam theory. Results are then compared with those obtained from numerical analysis method. The wind turbine tower deflection is found maximum at the tip of the structure and increasing with the hub height. Results indicate that the square cross-section tower is superior with respect to tower deflection with a maximum deflection of 0.064 mm. Numerical analysis method is used to verify the results of mathematical tower deflection model showing very less percentage of error. Thus, the new mathematical model has the advantage of estimating the tower deflection by just knowing the average wind speed of a wind farm for any wind turbine tower structure.