The level of tourism development is measured based on sales data of scenic spots on OTA platforms and the panel threshold regression model is applied to explore the impact of county-level tourism development on the urban-rural income gap and regional heterogeneity in the old revolutionary base areas of Hunan province from 2019 to 2021. The impact of tourism development on the income gap between urban and rural areas presents the dual threshold effect of an “N-shaped” pattern of “widening-shrinking-widening”. During the same development period, effect on the rural residents’ income is slightly greater than that on the urban residents’. The level of economic development of the counties directly affects the impact of tourism evolution on the disparity in income between urban and rural areas, and the growth of tourism in economically developed counties is more conducive to alleviating the disparity in income between urban and rural areas. The difference in the level of tourism development at the county level leads to the difference in its impact on the income gap. The inhibition effect of tourism development on the income gap between urban and rural areas is more obvious in tourism-developed counties. Consequently, local governments should formulate tourism development plans according to local conditions, actively explore diversified industrial revitalization mechanisms and cultivate and grow distinctive industries, and fully utilize the tourism linkage effect, thereby promoting the coordinated development of urban and rural areas.