Energy stock investor sentiment reflects the investment desires and expectations of investors and plays a significant role in the investment decision-making process and in asset value. There are many ways to measure investor sentiment; for example, the development of the Internet makes it possible to use the online comments of investors to portray their sentiments. Taking a complex network perspective, this paper selected the PetroChina Company Limited as the research object, obtained 96839 investor online comments and analyzed their emotional tendencies and sentiment transmission process. In addition, on this basis, we examined the relationship between investor sentiment and stock price volatility to analyze the transmission characteristics of investor sentiment. The results show that, overall, PetroChina investor sentiment experienced stable fluctuations over the past five years, and stock returns fluctuated within the range of investors' acceptable volatility. In addition, a weak positive correlation is found between investor sentiment and stock returns. The investor sentiment transmission network has scale-free characteristics and cluster effects. This paper is helpful for understanding the behavior of investors in the stock market, and it provides a new perspective on the relevance of unstructured text and structured data.