The invention provides a process method for preparing a potassic fertilizer by reaction of ammonia evaporation wastewater in a soda plant and potash feldspar, which comprises the following steps of: (1) taking ammonia evaporation waste liquor; (2) uniformly mixing the ammonia evaporation waste liquor and potash feldspar powder in a weight ratio of the total weight of CaCl2 and NaCl contained in the ammonia evaporation waste liquor to the weight of the potash feldspar powder of 0.05-0.2:1; and (3) roasting at the temperature of between 700 and 1,300 DEG C for 2 to 4 hours. The ammonia evaporation waste liquor is taken as a raw material and is changed into treasure, so the long-term influence of a large amount of ammonia evaporation waste liquor in the soda plant on the environment is radically eliminated, the whole production process has no secondary pollution, and the process method has good social benefit. In addition, the ammonia evaporation waste liquor is directly and effectively utilized to prepare water-soluble potassic fertilizers and KCl crystal materials, and has wide application range and obvious economic benefit. The process method has the advantages of simple process, low production cost and suitability for promotion and application.