Objective To study the differential effect of dermoscopy in nail psoriasis and onychomycosis. Methods A total of 31 patients with nail psoriasis admitted to Zhuxi County People's Hospital from January 2020 to December 2022 were selected as the control group, and 31 patients with onychomycosis admitted in the same period were selected as the study group. Dermatoscopy was performed in both groups. The results of clinical pathological diagnosis were used as the gold standard to analyze the differential effect of dermoscopy on nail psoriasis and onychomycosis, and to observe the detection of different lesion types by dermoscopy. Results There was no significant difference between the positive detection rate and the positive rate of pathological diagnosis in the two groups (P>0.05). There was no significant difference in the diagnostic accuracy of different lesion types between the two groups (P>0.05). Conclusion Dermatoscopy can not only accurately identify nail psoriasis and onychomycosis, but also accurately detect different lesion types, provide a reliable basis for the treatment of patients, and has definite clinical application value.