rainy是形容词，一般做定语，不作谓语，意思是“下雨的；多雨的；为雨所淋湿的；含雨的”。raining是动名词，既可以做定语又可以做谓语，意思是“雨；雨水；雨季；下雨；降雨”。
raining
1.It was raining when we set out. 我们出发时正下着雨。
2.Yesterday the radio forecast drizzle,and today it is indeed raining. 昨天预报有小雨，今天果然下起来了。
3.It's raining hard. 雨下得正急。
4.It's raining rustlingly. 雨刷刷地下起来了。
5.Hurry in,children.It's raining! 孩子们，快进来，下雨啦！
rainy
1.They walked along the promenade on a rainy night. 他们在一个雨夜沿着海滨道散步。
2.The rainy season in the Andes normally starts in December. 安第斯山区的雨季通常在12月份来临。
3.The rainy season has ended at last. 雨季总算过去了。
4.We may expect muggy weather when the rainy season begins. 雨季开始时，我们预料有闷热的天气。
5.In the rainy season things get damp easily. 雨季里东西容易返潮。