Socio-economic status plays a critical role in shaping unmet healthcare needs, and the COVID-19 pandemic has further intensified these disparities; however, research to date remains insufficient. Therefore, this study aims to analyze unmet healthcare needs by household income using large-scale longitudinal data (2010-2022) including pre- and post- pandemic differences. This large-scale study (n = 2,628,584) utilized nationwide data from the Korea Community Health Survey (KCHS) conducted between 2010 and 2022, administered by the Korea Disease Control and Prevention Agency. The analysis employed complex, weighted sampling to examine trends in unmet healthcare needs, with a specific focus on changes during the COVID-19 pandemic. Weighted logistic regression models were used to calculate odds ratios and β differences (βdiff) between the pre-pandemic (2010-2019) and pandemic (2020-2022) periods. In total, 2,628,584 individuals participated in the KCHS from 2010 to 2022, comprising 1,454,129 males (55.3%) and 1,174,455 females (44.7%). Before the pandemic, there was a consistent decline in the prevalence of unmet healthcare needs. However, following the onset of the pandemic, unmet healthcare needs increased (βdiff, low-level of household income: 1.66 [95% CI, 1.41-1.92]; mid-level of household income: 0.88 [95% CI, 0.77-0.99]; high-level of household income: 0.71 [95% CI, 0.57-0.85]). Overall, households with lower incomes exhibited higher levels of unmet healthcare needs compared to those with higher incomes (low household income: 14.8 [95% CI, 13.91-14.24]; high household income: 8.45 [95% CI, 8.34-8.55]). Additionally, the disparity in healthcare access due to income differences was more pronounced among older individuals, those with lower educational attainment, and those with lower subjective health status. Our analysis found that older adults in low-income households consistently faced higher rates of unmet healthcare needs. The reversal of a pre-pandemic trend toward reducing healthcare gaps highlights the urgent need for targeted interventions to address socio-economic disparities.