Recently, creating unnatural fluorescent nucleobase analogues has gained increasing attention. In this work, a detailed computational investigation on the photophysical properties of the fluorescent adenine analogue x-adenine (xA) is carried out. The ten lowest low-lying exited states are analyzed and assigned. The effects of methanol solution, linking to deoxyribose, and base pairing on its absorption and emission processes are considered. The calculated excitation and emission energies are in good agreement with the measured data available. It is found that linking to deoxyribose and methanol solution have a hyperchromic effect on xA. Also it is found that methanol solution and linking to deoxyribose will lead to the red shift of fluorescence, while base pairing does not have obvious effects on the lowest ππ* state and fluorescence emission but produces the blue shift of lowest nπ* to some extent.