This study investigates the correlation between textual ideology and the English translations of political discourse. It focuses on how the translation shifts of modality relate to the socio-political and socio-cultural context of Chinese political discourse using the modality system of Systemic Functional Linguistics (SFL) as the theoretical framework. Three main types of translation shifts between should and will, and their corresponding items are identified. First, the addition of modal items should and will in the TTs; second, downgrading the modality value of Chinese modality items to the lower-valued should and will in the TTs; third, upgrading the modality value of Chinese modality items to a higher-valued will in the TTs. The study attributes these findings to van Dijk’s ideological square model and the variable of tenor (the social distance between the speaker and the addresses and the social distance between the official translators of Chinese political discourse and the international audience.