Intangible cultural heritage (ICH) is a keystone of sustainable development which, in recent years, has received growing attention from scholars and governments. Previous studies on ICH collaborative protection have focused on ICH connotations and practice, but relatively few studies have focused on the interrelationships among the influencing factors of the collaboration effect. This study introduces a new variable, relationship quality, in an effort to describe the collaborative relationship among participants. The collaborative relationship consists of three dimensions: trust, communication, and fairness. Regarding relationship quality as an intermediary variable, we construct a research framework embracing participant subject factors (collaboration attitude and collaboration ability) and collaboration effects in a case study on collaborative protection of ICH in Regong Thangka, China. A structural equation model, for which data were collected via a questionnaire, is used to assess the strength of the relationships among variables. A total of 416 questionnaires were distributed, and 365 valid completed questionnaires were returned. The findings indicate that relationship quality has a significant influence on collaboration effects in the collaborative protection of ICH. Within the study’s context, collaboration attitude has a significantly positive impact on relationship quality, and it indirectly influences collaboration effects via relationship quality. Collaboration ability has a significantly positive impact on relationship quality and collaboration effects, and it could also impact collaboration effects indirectly via relationship quality. This paper is the first to introduce the concept of relationship quality into the ICH collaborative protection research field, and its findings may have valuable theoretical and practical implications.