In-depth analysis and discussion of the interactive relationship between urbanization and ecological security are basis and prerequisite for ensuring the coordinated development of urbanization and ecological protection. This paper constructed the evaluation index system of urbanization level from four dimensions (i.e., population, economy, society, space) and ecological safety from three aspects (i.e., pressure, governance, environment). Then, the Urbanization Development Index (UDI) and Ecological Security Index (ESI) of the nine provinces along the Yellow River were calculated, and grey relationship and decoupling model were employed to study the interaction between urbanization and ecological security from 2008 to 2018. The main conclusions are as follows: a) The urbanization level and ecological security level of the nine provinces along the Yellow River show an overall upward trend while the increase rate gradually slows down, in which UDI and ESI increases from 0.24 to 0.58 and 0.30 to 0.41 respectively. b) The correlation degree between the urbanization level and the ecological security system is higher than 0.6, which is between the medium correlation and the extremely strong correlation. Population urbanization has the greatest impact on ecological security, with a correlation value of 0.74. Ecological governance has the strongest restraint on urbanization development and the correlation value is 0.72. c) There is a strong decoupling effect between urbanization and ecological security in the nine provinces along the Yellow River, and the future ecological security will gradually become more restrictive on the development of urbanization.
