The difficulty of travel for the elderly is a challenge for urban management. Quantifying the satisfaction of public transport services from the perspective of the elderly is a people-oriented scientific research method. Based on the survey data of 2019 and 2020 and by selecting the interview data of people over retirement age before analyzing the non-linear relationship between bus service elements and elderly satisfaction by the impact-asymmetry analysis and gradient boosting decision trees, the optimization strategy of ground public transportation for the elderly in Harbin was obtained. The results show that the following five factors have the greatest impact on overall satisfaction, namely, site broadcasting, complaint handling, awning facilities, driver driving habits, and the punctuality of bus operation. Among them, “awning,” the “punctuality of bus operation,” and “drivers’ driving habits” should be given priority to improve. The conclusion of this study provides a theoretical basis for the accurate optimization of public transport services.