Objective To explore the change track of prognostic nutritional index in patients with primary liver cancer and analyze its influencing factors. Method 140 patients diagnosed with primary liver cancer who underwent surgical treatment in the Third People's Hospital of Nantong from January 2021 to December 2023 were selected as the study objects. General data questionnaire and nutritional index were used to investigate within one week after surgery T1 after the first radiotherapy T2 after 15 radiotherapy T3 after 30 radiotherapy or after the last radiotherapy T4 . Latent category growth model and single factor analysis were used for data processing. Result The prognostic nutritional index curve of patients with primary liver cancer was identified to be divided into three potential categories and the average probability of patients in each category belonging to each potential category was 0. 946 0. 950 0. 944 respectively. The three categories were malnutrition plus recombination 28. 3% good nutrition 55. 8% and improved malnutrition 15. 9% . Different locus categories were age χ 2 = 15. 025 P = 0. 005 marital status χ 2 = 7. 407 P = 0. 025 education level χ 2 = 16. 364 P= 0. 012 liver cancer grade χ 2 = 12. 004 P= 0. 017 chronic disease χ 2 = 7. 887 P= 0. 012 the difference was statistically significant. Conclusion By investigating the change characteristics of prognostic nutritional index in patients with primary liver cancer from postoperative to the end of radiotherapy this study identified three different curve trajectories and there were differences in the curve trajectories of prognostic nutritional index in patients. Clinical staff should pay close attention to patients with primary liver cancer caused by malnutrition and recombination timely identify high-risk patients with malnutrition and provide active and targeted nutritional support to reduce the occurrence of adverse events caused by malnutrition as much as possible.