Objective To explore the treatment decision-making process of cancer patients, and to provide evidence for helping cancer patients make high-quality treatment decisions. Methods Totally, 12 cancer patients were interviewed in depth, and the data were coded by Strass and Corbin grounded theory, then categories and core categories were formed. Results A core category, namely the trajectory of cancer patients′ treatment decision-making, was extracted. The trajectory went through 6 periods (information fusion, dependence and compromise, analysis and evaluation, intention formation, conclusion in decision-making, and chain reaction), and was influenced by two forces, namely decision-making motivation and decision-making resistance. Conclusion Diversity in information is the reference for decision-making; independence is the basic guarantee of decision-making; prudence is an important strategy for decision-making; sustained response is the long-term direction of decision-making.Medical staff should understand the trajectory of cancer patients′ treatment decisions, and then help them make scientific, effective and high-quality treatment decisions smoothly.