Background: Among Chinese college students, the burden of depression is considerably high, affecting up to 30 % of the population. Despite this burden, few Chinese students seek mental health treatment. In addition, depression is highly comorbid with other mental health disorders, such as anxiety. Scalable, transdiagnostic, evidence-based interventions are needed for this population. Objective: The study will evaluate the effectiveness of a World Health Organization transdiagnostic digital mental health intervention, Step-by-Step, to reduce depressive and anxiety symptoms and improve well-being compared with enhanced care as usual and its implementation in a Chinese university community. Methods: A type 1 effectiveness-implementation two-arm, parallel, randomized controlled trial will be conducted. The two conditions are 1) the 5-session Step-by-Step program with minimal guidance by trained peer-helpers and 2) psychoeducational information on depression and anxiety and referrals to local community services. A total of 334 Chinese university students will be randomized with a 1:1 ratio to either of the two groups. Depression, anxiety, wellbeing, and client defined problems will be assessed at pre-intervention, post-intervention, and 3-month follow-up. Endline qualitative interviews and focus group discussions will be conducted to explore SbS implementation among service users, university staff, and stakeholders. Data will be analysed based on the intent-to-treat principle. Discussion: Step-by-Step is an innovative approach to address common mental health problems in populations with sufficient digital literacy. It is a promising intervention that can be embedded to scale mental health services within a university setting. It is anticipated that after successful evaluation of the program and its implementation in the type 1 hybrid design RCT study, Step-by-Step can be scaled and maintained as a low-intensity treatment in universities, and potentially extended to other populations within the Chinese community. Trial registration: ChiCTR2100050214.