In the digital era, cities globally are leveraging symbolic resources for city branding through social media. This study delves into how Hangzhou, a burgeoning first-tier city in China, constructs its international image on YouTube. A semiotic framework is established to conceptualize Hangzhou's city branding, exploring how evaluative attributes take effect through verbal, visual, and auditory elements in 83 YouTube videos. Verbal articulation is further divided into explicit and implicit forms. Visual embedding includes depictions of sceneries, characters, and effects. Auditory embeddings also have two parts: depictions of voiceovers and signs. Posted by the official account of Hangzhou's cultural and tourism bureau, these videos from the Asian Games period depict Hangzhou viewing the sports event as a valuable opportunity for external promotion. Analyzing 123 evaluative attributes among videos reveals Hangzhou's dual identity as both modernity and historicity. Results show that the modern metropolis image portrays Hangzhou as a cosmopolitan, vibrant, high-tech, and sustainable city, while the historical city image is crafted through the recreation of ancient cultural scenes and the revitalization of folk traditions. The characteristics of multimodal critical discourse reflect China's sports diplomacy and the affordances of social media. By examining the communication situation, this paper will give suggestions to Chinese cities about building a positive and influential image and enhancing China's international communication capabilities.