Introduction: The Health System Development Project is one of the performance-based financing strategies in the Democratic Republic of the Congo, in line with the national health development plan and universal health coverage. This study was conducted to assess the contribution of the Health System Development Project to the financial accessibility of healthcare for households in the Masina 1 health zone. Methods: This study is quasi-experimental and employed a quantitative approach. It was conducted in three health areas of the Masina 1 health zone, which is supported by the Health System Development Project, and two health areas of the N’djili health zone, which is not supported, covering the period from 2017 to 2021. The sample consisted of 403 household heads, including 243 from the Masina 1 health zone and 160 from N’djili. Data were collected through interviews. Bivariate analysis was performed using SPSS and STATA software with a significance level of 0.05. Results: Support from the Health System Development Project made healthcare financially accessible to households in the Masina 1 health zone, with 4.2 times higher accessibility compared to those in the unsupported N’djili health zone (OR = 4.2 [3.8–4.5]). The results indicate that from 2019 to 2021, project support improved coverage in CPS by 23.79%, deliveries by 10.88%, curative care by 6.71%, first prenatal consultation (CPN 1) by 2.16%, fourth prenatal consultation (CPN 4) by 4.2%, health facility revenue by 3.32%, and health facility MEG capital by 7.55% in Masina 1. Conclusion: With support from the Health System Development Project, households in the Masina 1 health zone became 4.2 times more financially able to access healthcare compared to those in the N’djili health zone, which does not receive support.