Transcranial focused ultrasound is a non-invasive stimulation modality delivering mechanical energy to deeper brain regions in the form of an acoustic pressure wave, which can result in numerous bioeffects. Computational techniques and models are becoming increasingly relevant to creating and optimising stimulation devices, treatment efficacy, safety evaluation, and improving knowledge of the underlying physical and physiological mechanisms. They provide a high level of control and ease the investigation of enormous parameter spaces. This thesis is to numerically investigate the applications of transcranial focused ultrasound based on detailed human head models constructed from medical images. Specifically, the influence of energy distribution within the brain tissues was studied using customised, focused ultrasound transducers. Secondly, the mechanical and cavitation indexes, as two metrics reflecting ultrasound-induced brain blood barrier disruption, are used to analyse the changes in intracranial fields. Thirdly, the effects of low-intensity focused ultrasound with dual single-element transducers in beam profiles, including the volume of full width at half maximum, and axial and lateral directions of the focal area, were investigated. Fourthly, the influence of the skull effects, including the different transducer placements on the head and differences between 0.35 MHz and 0.5 MHz acoustic frequency for both female and male models, was studied. The outcomes of this study suggest that a suitable combination of transducer size, location, and power level can achieve the most promising performance based on location in the brain. In addition, the numerical studies in this project provide a valuable method for highly detailed and specific non-invasive brain stimulation using focused ultrasound stimulation, which could be further explored and utilized in future research applications and clinical practices.