Abstract: Due to the characteristics of low threshold and high freedom,open source software encounters slow progress,low efficiency and low quality in the development process.Software cliff wall as a criterion of project robustness,indicates unexpected acceleration in common incremental development activities over short periods of time,which is a potential threat to the sustainable development in software evolution.Therefore,analyzing the causes of software cliff walls is an effective method to deeply understand the development process of open source projects,to more accurately describe the evolution of software,and to improve the efficiency of software development.The experiment firstly constructes a series of developer collaboration networks (DCNs) over more than 150 thousand commits from 9 GitHub projects by month and quarter respectively.This paper consideres a single commit of more than 10 000 lines of code as a software cliffs.And then it introduces 9 metrics,such as the number of nodes,the number of connected edges,the node update rate,the module degree,the average path length,the average degree,the node penetration index,the node out-of-mean,and the diversity,to analyze the relationship between DCN and cliff walls from the perspectives of network scale,network structure and network quality.The results show that:1)smaller development teams and greater member turnover tend to cause a cliff wall;2)‘small world’ features among developers is helpful to avoid the emergence of software cliff walls;3)the relationship between DCN and software cliffs in the software development process is more appropriate in a quarterly cycle,and the diversity of the development team will also affect the creation of cliff walls in software development.

Key words: Developer collaboration network, Group collective development, Open source software, Software cliff walls, Software evolution