amelioration       
noun [ U ] uk/əˌmiː.li.əˈreɪ.ʃən/ us/əˌmiː.li.əˈreɪ.ʃən/
 改善|减轻
the process of making a bad or unpleasant situation better
  Regular exercise can provide gradual amelioration of anxiety. 定期锻炼可以逐渐减少焦虑 
 Treatment for her allergies led to the amelioration of her symptoms. 针对她的过敏的治疗使症状得以减轻。 
 See: ameliorate
 - More examples
 - The most that could be hoped for in the 1920s was the amelioration of a small number of the worst houses.
 - We've seen some amelioration of atmospheric greenhouse gas emissions.
 - Several programmes are aimed at amelioration of the industrial pollution of the creek.