As the main form of urban outdoor environment, urban public open space is of great practical significance in meeting residents’ leisure and fun needs. There is a contradiction between the need to improve the quality of urban open space and the difficulty of existing open space to meet the needs of different age groups for equal sharing and diversified activities. Starting from the concept of playful city, the study rethinks the city in terms of human orientation, takes the evaluation of spatial playfulness as an essential way to improve spatial quality, extracts 25 indicators of all-age playfulness evaluation of urban public open space through literature analysis and questionnaire survey, constructs the evaluation system of all-age playfulness by using the Q-method, and takes three urban public open spaces in Shanghai as examples to carry out empirical investigation on the evaluation system of all-age playfulness, analyzing the current situation of all-age playfulness, and analyzing the current situation of all-age playfulness. The study examines the current level of all-age playfulness and proposes a corresponding optimization path. The study’s results are intended to provide references and bases for assessing the current situation of all-age playfulness in urban public open spaces, as well as for the decision-making of planning, design, and spatial optimization and upgrading.