Introduction Mild cognitive impairment (MCI) is an intermediate phase between normal cognitive ageing and dementia and poses a serious threat to public health worldwide; however, it might be reversible, representing the best opportunity for secondary prevention against serious cognitive impairment. As a non-pharmacological intervention for those patients, interventions that combine physical exercise and cognitive training, whether delivered simultaneously or sequentially, may have superior effects on various cognitive domains, including global cognition, memory, executive function and attention. The supportive evidence remains incomplete. This study aims to assess the effectiveness of a combined exercise and cognitive intervention in Chinese older adults with mild cognitive impairment (COGITO), empowered by digital therapy and guided by the Health Action Process Model and the Theory of Planned Behaviour (HAPA-TPB theory) in a home-based setting. Methods and analysis This study is a randomised controlled, assessor-blinded multi-centre study. Four parallel groups will include a total of 160 patients, receiving either a combined exercise and cognitive intervention, an isolated exercise intervention, an isolated cognitive intervention or only health education. These interventions will be conducted at least twice a week for 50 min each session, over 3 months. All interventions will be delivered at home and remotely monitored through RehabApp and Mini-programme, along with an arm-worn heart rate telemetry device. Specifically, supervisors will receive participants’ real-time training diaries, heart rates or other online monitoring data and then provide weekly telephone calls and monthly home visits to encourage participants to complete their tasks and address any difficulties based on their training information. Eligible participants are community-dwelling patients with no regular exercise habit and diagnosed with MCI. The primary outcome is cognitive function assessed by the Alzheimer’s Disease Assessment Scale-Cognitive (ADAS-Cog) and Community Screening Instrument for Dementia (CSI-D), with baseline and three follow-up assessments. Secondary outcomes include quality of life, physical fitness, sleep quality, intrinsic capacity, frailty, social support, adherence, cost-effectiveness and cost-benefit. Ethics and dissemination The study was approved by the Institutional Review Board of Peking University. Research findings will be presented to stakeholders and published in peer-reviewed journals and at provincial, national and international conferences. Trial registration number ChiCTR2300073900.