This paper studies the data preprocessing and analysis methods of the key microwave ranging system for the low-low satellite-to-satellite tracking gravity mission, and achieve the efficient suppression of the key carrier frequency noise, as well as the elimination and correction of the related interference and deviation. According to the theoretical analysis results, relevant processing and analysis procedures are developed. The residual between the dual one-way ranging data product completed by this research and the official product of GRACE Follow-On is much smaller than the design requirement of the payload, which meets the accuracy requirements of gravity field inversion. Evaluation and analysis methods for electronic noise, system noise and other noise in the final data product are discussed. In this paper, by introducing the frequencydomain analysis method of the spatial inhomogeneity of the ionospheric free electron content, and using the inter-satellite microwave ranging data, the ability to analyse the variation behaviour of free electron content at different spatial scales and its global distribution characteristics is realized, providing data support for the in-depth study of the ionosphere. This research can provide relevant technical accumulation and reference for the data preprocessing and analysis of the microwave ranging system for low-low satellite-to-satellite tracking missions of China.