Abstract: The exploitation and utilization of water resources have changed the natural hydrological regime of rivers and impacted the ecological environments of rivers.Ensuring a suitable ecological flow is crucial for the preservation of river ecosystems.Considering the runoff inconsistencies and the data redundancy, we employ the M-K method, Cumulative Offset Verification and the PCA-IHA index system to evaluate the alteration degree of a hydrological regime more accurately.A comprehensive ecological flow suitability evaluation system is established based on the hydrological method of ecological flow calculation.We propose three evaluation indexes such as the threshold interval guarantee rate, deviation index, and standard compliance rate, and then establish a suitability index synthetically.The application of this system to the mainstream of the Ganjiang River revealed that:(1) The alteration degree of the hydrological regime in the Ganjiang River mainstream from 1960 to 2015 was low, with a variation point in 1991.(2) Each hydrological method has its strengths and weaknesses in the proposed evaluation index, and the suitability index varies significantly, which indicates that this evaluation system can effectively filter out the calculation method most suitable for the study area.In the case of the Ganjiang River mainstream, the most suitable method is the monthly frequency method, with a suitability index of 0.8.The research results can provide a scientific reference for improving the suitability evaluation system of ecological flow.