Objective To compare the effect of different doses of compound betamethasone intradermal block on post-herpetic neuralgia (PHN) in elderly patients. Methods Between June 2013 and December 2014, 96 elderly patients who matched the criteria of PHN were chosen and randomly divided into saline control group (group C), compound betamethasone 0.5 mL group (group B0.5) and compound betamethasone 1.0 mL group (group B1.0). For the control group, 20 mL analgesic saline liquid including 5 mL of 2% lidocaine was used. And 0.5 and 1.0 mL compound betamethasone was added into the solution of group C to get the solution for group B0.5 and group B1.0, respectively. The patients got intracutaneous injection once in the affected area on the day 1, 8, and 15 respectively, and patients in the same group were injected the same solution of analgesic liquid. All the patients took the same medicine during treatment. Their visual analog scale (VAS) scores, quality of sleep (QS) scores and adverse events before treatment (T0), at discharging from the hospital (T1), and three months after discharging (T2) were carefully noted and analyzed. Results The VAS and QS scores of the three groups at T1 and T2 improved significantly compared with those at T0 (P < 0.05). The VAS and QS scores of group B0.5 and group B1.0 improved significantly more compared with group C (P < 0.05), and the difference of VAS and QS scores between group B0.5 and group B1.0 was not statistically insignificant (P > 0.05). Conclusions Adding 0.5 mL or 1 mL of compound betamethasone to the 20 mL analgesic liquid for intradermal block treatment on PHN can obviously release patients’ pain and improve their sleep quality. Compared with 1 mL, adding 0.5 mL compound betamethasone to the 20 mL analgesic liquid for intradermal block treatment on PHN is a more ideal dose.