Objective To explore the value of skin light transmission microscope (dermoscopy) in the diagnosis of skin erythematous diseases. Methods A total of 121 patients with skin erythema disease who were treated in Kaiyang County Hospital of Integrated Traditional Chinese and Western Medicine from January 2023 to June 2024 were selected as the research objects. All of them were examined by macroscopic observation and dermoscopy. Naked eye observation was the control group, and dermoscopy was the observation group. The detection rate and examination time of the two groups were compared. Results The detection rates of psoriasis, allergic dermatitis, exogenous photosensitivity dermatitis, and erythema multiforme in the observation group were 100.00%, 100.00%, 100.00%, and 87.50%, which were higher than 70.59%, 60.00%, 30.00%, 25.00% in the control group (χ 2=6.315, 8.000, 10.769, 6.349, P =0.012, 0.005, 0.007, 0.012). The examination time of the observation group was (5.56±0.78)min, which was lower than that of the control group (5.61±0.81)min, but the difference was not statistically significant (t =0.489, P =0.625). Conclusion The value of skin surface light transmission microscope (dermoscopy) in the diagnosis of skin erythematous diseases is accurate, which can improve the detection rate of the disease, and the examination time is equivalent to that of the naked eye. It is worthy of clinical application.