Skin computed tomography (CT) image based on improved marching cubes (MC) algorithm was explored to evaluate the therapeutic effect of internal administration of Liangxue Xiaoyin decoction combined with medicated bath in the treatment of psoriasis vulgaris. 712 patients with psoriasis vulgaris blood heat syndrome in hospital were recruited as the research object, which were randomly divided into observation group (TCM oral therapy combined with medicinal bath) and control group (TCM oral therapy), each with 356 cases. Psoriasis area and severity index (PASI), pruritus degree, and clinical treatment effect were compared. The results showed that the reconstruction time of median method was greatly shorter, and the algorithm efficiency was improved by 40.6290%. After treatment, the psoriasis area and severity index (PASI) score of the observation group was 5.61 ± 1.15 , Δ PASI = 22.64 ± 2.15 . Δ PASI % = 80.14 % , which were greatly higher than the control group (( 9.41 + 1.56 ) points, Δ PASI = 18.84 + 1.65 points, Δ PASI % = 66.69 % ) ( P < 0.05 ). After treatment, the itching degree of the observation group was 3.03 ± 1.01 points, which was lower than that of the control group (( 3.71 ± 1.06 ) points), and the itching degree of the observation group was greater than that of the control group, with substantial difference ( P < 0.05 ). The total effective rate of observation group (88.76%) was higher than that of control group (71.07%) ( P < 0.05 ). Therefore, skin CT image based on the improved MC algorithm can evaluate the therapeutic effect of internal administration of Liangxue Xiaoyin decoction combined with medicated bath in the treatment of psoriasis vulgaris. The internal administration of Liangxue Xiaoyin decoction combined with medicated bath had a good effect on the treatment of psoriasis vulgaris and was of certain clinical application value.