Dementia affects not only the patients, but also the caregivers. Timely targeted supporting for informal caregivers of people with dementia can improve their health and life quality, as well as contribute to sustainable healthcare. However, which interventions could efficiently support them and why still remains unclear. This systematic review aims to close this gap by critically assessing the current state of randomized controlled evidence concerning informal caregivers of older people with early dementia. We searched the electronic databases PubMed, CINAHL, Embase, Cochrane and Web of Science and assessed the methodological quality of the selected studies using the validated PEDro scale. A total of 2067 studies were identified in the initial searching, and 29 randomized controlled studies were finally selected based on the rigorous inclusion and exclusion criteria. Through completely assessing the methodological quality of studies, and the essentials and effectiveness of the 22 different types of interventions, we identified which interventions were effective and why. Timely targeted interventions for this caregiver group remains scarce. Furthermore, we highlight that there is a lack of systematic caregiver needs assessments prior to or when delivering the interventions.