Anaerobic ammonia oxidation (anammox) granular sludge was used to treat simulated saline wastewater, and the effect and mechanism of sheep manure biochar (SMB) addition on the enhancement of nitrogen removal performance when the process was inhibited by high salinity were investigated. The results showed that the nitrogen removal effect deteriorated with increasing salinity as influent salinity reached 2% and above. With a one-time addition of 5 g/L SMB, the reactors inhibited by 2% and 3% influent salinity were able to recover their nitrogen removal performance after 18 and 34 days of operation, respectively, and the total nitrogen (TN) removal efficiencies were stabilized at 90% or more. At an influent salinity of 4%, the TN removal efficiency recovered to over 70% after dosing 5 g/L of SMB twice and running for 43 days. For an influent salinity of 5%, the relief of salinity inhibition by increasing the amount and frequency of SMB dosing was not significant. With its abundant pore structure and rich surface functional groups, SMB created favorable conditions for promoting microbial attachment and growth, extracellular polymeric substances secretion, sludge-specific anammox activity, and electron transfer activity. The moderate dosing of SMB can effectively alleviate the inhibitory effect of high salinity on nitrogen removal and provide a useful strategy for the efficient application of the anammox process in saline wastewater treatment.