Unraveling the tectonic geomorphological processes along the northeastern margin of the Tibetan Plateau (NETP) is essential for understanding the mechanisms of the plateau's uplift and growth. Previous studies, utilizing low-temperature thermochronology, have illuminated the erosional dynamics along the fault zones, thereby revealing the Cenozoic northeastward expansion of the Tibetan Plateau. However, sparse low-temperature thermochronological data from inter-fault block areas which exhibit pre-Cenozoic ages, appear to lack a record of the northeastward expansion of the Plateau. To further elucidate the uplift and erosional history of the relatively stable inter-fault block regions within the NETP, this study focuses on granite massifs in Longyang gorge and rock bodies promximal to the headwaters of the Hudan River, situated to the east of Qinghai Lake. Analyzed through apatite fission track, six samples were utilized to reconstruct the thermal history of the study areas. In addition, the steady-state vertical exhumation rates and eroded thickness since the middle Miocene was calculated using Age2exhume. Our findings reveal: (1) A pronounced phase of rapid cooling since <10 Ma, indicating the ongoing northeastward expansion of the plateau; (2) Elevated erosion rates and significant eroded thickness within the Laji Mountain-Jishi mountains region, influenced by robust fault activity since the middle Miocene. The integration of low-temperature thermochronological ages with sophisticated thermal history simulation techniques has shed new light on the uplift and erosional history of the stable inter-fault blocks in the NETP, thereby providing new evidence for the plateau's sustained expansion since the middle Miocene.