To limit global warming below 1.5–2°C, 140+ countries pledged carbon neutrality. However, many less-developed countries and regions face economic constraints and often suffer from severe ecosystem degradation, which jointly hinder their ability to meet these commitments. Here, we used the Qinghai-Tibet Plateau (QTP), a less-developed region that has experienced ecosystem degradation, as a case study. Using a novel multi-scenario modelling framework to assess the impact of different combinations between natural climate solutions (NCS) and carbon emission reduction policies (CERP) on carbon neutrality and associated costs. Our findings show that carbon neutrality was achieved on the QTP by 2020, with a surplus of 18.16 MtCO₂/yr. However, without CERP, carbon emissions on the QTP are projected to increase fivefold by 2060 compared to 2020 levels. Even with stringent NCS, nearly 375.34±99.05 MtCO2/yr shortfall in maintaining carbon neutrality remains in 2060. If CERP are implemented without NCS, the cost of maintaining carbon neutrality in 2060 is estimated at US$ 199.07±25.96 billion during 2020-2060. Notably, integrating NCS with CERP reduces costs by nearly half (US$ 111.51±21.48 billion). Furthermore, the integration of aggressive CERP and NCS on the QTP could contribute more additional surplus by 2060 toward national carbon neutrality goals at pretty lower carbon price. Our research highlights that combining NCS with CERP yields greater climate benefits at significantly lower costs, providing potential pathways for financially constrained regions to enhance climate mitigation, especially when supported by international climate finance and cooperative mechanisms.