Objective To analyze the vitamin deficiency of hospitalized cancer patients explore the correlation between vitamin deficiency and nutritional risk and malnutrition and provide scientific reference basis for nutritional intervention of cancer patients. Method A total of 1257 cancer patients in our hospital from August 2021 to June 2022 were selected vitamins were determined using Qlife Lab 9000plus liquid chromatography triple quadrupole tandem mass spectrometer to analyze the proportion of various vitamin deficiencies. Nutritional risk screening 2002 was used for nutritional risk screening and the Global Leadership Initiative on Malnutrition standard was used for the diagnosis of malnutrition. Analyze the correlation between nutritional risk or malnutrition and vitamin deficiency. Result The average age of 1257 cancer patients was 59. 71 ± 11. 17 years old. There were 783 males and 474 females with an average body mass index of 23. 35 ± 3. 62 kg / m 2 . The incidence of nutritional risk was 35. 88% NRS 2002 ≥ 3 points and the incidence of malnutrition was 22. 12% . All water - soluble vitamins are deficient with varying degrees with vitamin B1 deficiency accounting for the most 80. 9% and vitamin B3 deficiency accounting for the least 1. 4% . Fat soluble vitamins were deficient in vitamin D alone accounting for 89. 4%. Compared with patients without nutritional risk there was a statistically significant difference in the proportion of vitamin A and vitamin C deficiency among patients with nutritional risk 39% vs. 45. 5% P<0. 05 . Compared with patients without malnutrition there was a statistically significant difference in the proportion of vitamin A and folic acid deficiency among patients with malnutrition 55. 1% vs. 47. 6% P<0. 05 . Conclusion The proportion of vitamin D vitamin B1 folic acid and vitamin C deficiency in hospitalized cancer patients was high. The nutritional evaluation of cancer patients should consider the vitamin levels to guide rational vitamin supplementation in clinic.