BACKGROUND: HIV self-testing (HIVST) offers potential solutions to challenges associated with site-based HIV testing (SBHT). However, the effectiveness of HIVST as an HIV prevention strategy for men who have sex with men (MSM) discontinuing pre-exposure prophylaxis (PrEP) after the completion of PrEP demonstration project has rarely been assessed. METHODS: The China Real-world Study of Oral PrEP (CROPrEP) project was conducted in four cities in China. Participants were directed to community resources to continue their PrEP medication after the discontinuation of project-provided PrEP at the last CROPrEP visit. We conducted a multicentre open-label randomized controlled trial among MSM who had discontinued PrEP induced by the completion of CROPrEP. Eligible participants were randomly assigned to either the intervention group or the control group (1:1). Participants received regular health education and behavioural interventions throughout the trial. The intervention group was given a link to order free HIVST kits online, while the control group received information about free SBHT. Both groups completed internet-based follow-up surveys at three and six months. The primary outcome was the proportion of participants who underwent HIV testing during the six-month follow-up period. This trial was registered at chictr.org.cn (ChiCTR2000038416). FINDINGS: Between November 2020 and January 2021, we recruited a total of 620 participants (300 in the intervention group and 320 in the control group). The follow-up completion rates were 99·0% and 95·0% in the intervention and control groups, respectively. At baseline, the median age of participants was 32 (interquartile range: 26-37), and 77·7% underwent HIV testing in the past three months. The proportion of participants who underwent HIV testing in the past three months was higher in the intervention group than in the control group at both the three-month (adjusted risk difference [RD]: 36·7, 95% confidence interval [CI]: 35·1-38·5, p < 0·001) and six-month (RD: 26·7, 95% CI: 24·6-28·7 p < 0·001) follow-up periods. INTERPRETATION: Our study suggests that providing online distribution of HIVST kits for MSM with PrEP discontinuation induced by completion of the PrEP project effectively promoted HIV testing. This digital approach improves access to HIV testing for MSM and can be applicable to other settings where MSM turn to online public health services. FUNDING: The study was funded by the Fund of National Natural Science Foundation of China; the Mega-Projects of National Science Research for the 13th Five-Year Plan; and the Liaoning Revitalization Talents Program, China.