The invention relates to an ammonia evaporation wastewater index control method and an ammonia evaporation wastewater index control device. The method comprises the following steps of: regulating ammonia evaporation alkali amount according to the type of an ammonia evaporation tower and the real-time detection result of the ammonia evaporation wastewater, controlling the pH value of the ammonia evaporation wastewater to be between 7 and 9, and controlling steam pressure, bottom temperature of the ammonia evaporation tower and top temperature of a dephlegmator through a steam pressure stabilizing valve so as to realize decomposition and denitrification of NH4<+> ions. The steam pressure and various parameters of the ammonia evaporation tower and the yield of pyridine are stable, the ammonia nitrogen qualification rate of the ammonia evaporation wastewater reaches 100 percent, the ammonia nitrogen content of the wastewater is between 30 and 150mg/L, environmental pollution is reduced, and a part of ammonia evaporation wastewater is recycled; and the tower blocking probability is reduced, the overhauling period of the ammonia evaporation tower is prolonged by 6 months, the overhauling expense is saved, and the labor intensity of maintenance personnel is reduced. The device is simple in structure, low in investment and quick in response; and the method is scientific, reasonable and convenient to master and operate, and has great popularization and use value.