<p>Quality of life (QoL) plays a crucial role in child development and emotional distress is common among adolescents. Emotions are natural responses to circumstances, and they change over time. Thus, individuals’ beliefs about the changeability of emotions, particularly negative emotions, matter. Mindsets about negative emotions (i.e., negative emotion mindsets) are interrelated with QoL; however, few studies have studied this association. Hence, this study aimed to examine the longitudinal reciprocal relationships between mindsets about anxiety, depression, and stress and QoL. A total of 3,748 participants (357 in Grades 4 and 5 and 3,391 in Grades 7–10, age range: 10–20&#xa0;years, age mean = 14.10&#xa0;years, <i>SD</i> = 1.62; boys <i>n</i> = 1,591, 42.4%) participated in a two-wave survey with a one-year interval. We measured demographic factors; family economic conditions; life satisfaction; negative emotion mindsets; and symptoms indexed by depression, anxiety, and stress. Cross-lagged panel model (CLPM) analyses were conducted to examine the reciprocal relationships between negative emotion mindsets and QoL (including life satisfaction and mental health symptoms). Results showed that the belief that negative emotional states could be changed at Time 1 predicted better QoL at Time 2. In addition, QoL measured at Time 1 predicted growth mindsets of negative emotional states at Time 2. Subgroup analyses based on sex showed that the relationship between mindsets and life satisfaction among boys was unidirectional, whereas it was bidirectional among girls. These novel findings in the Chinese context highlight the belief about the changeability of negative emotions as a promising factor for promoting QoL among children and adolescents.</p>