Objective To investigate the content characteristics and main influencing factors of patient complaints in online medical consultation. Methods Online medical consultation data from 2020 to 2024 were collected from an internet hospital platform of a tertiary hospital in Jiangsu Province. Valid complaint texts were analyzed using latent Dirichlet allocation topic modeling. Results A total of 176 309 valid consultation records were included, including 5 872 valid complaint texts. The overall complaint rate for online consultations was 3.3%. Complaints were primarily concentrated on low responsiveness, complex service processes, and insufficient professional quality, with “no response” accounting for the highest proportion (40.4%). There were statistically significant differences in complaint rates among different genders, ages, consultation departments, consultation fees, and consultation years (P<0.05). Conclusions Patient complaints in online medical consultations show clear structural characteristics. Optimizing physician responsiveness, simplifying service processes, and enhancing professional communication skills are important strategies to reduce complaint risks.