地 is objective. It describes situations as a fact. It also describes a state of an action, i.e: 他慢慢地吃 - he eats slowly [at a slow pace] 高兴地跳起来 = jump happily[jump in excitement] the sentence order is usually: adjective + 地 + verb 得 is subjective. It is more of an [opinionated] result of an action. 我已经吃完了，你吃得很慢 = I've already finished eating, you eat so slow!　[in my opinion] 意大利面做得很好吃 = the spaghetti was cooked well. [in my opinion] 他德语说得很好＝　he speaks German well! [in my opinion] Here, the sentence pattern is reversed. It is: verb + 得 + adjective 得 also has two other pronounciations: 我得赶快走！(wǒ děi gǎnkuài zǒu)- I must leave quickly! 他得了八十分 (tā dé le bā shí fēn)- he recieved 80 points.

They have the same meaning, that is he walks very fast. but we usually say 他走得很快，not他快地走。他走得快 emphasizes his speed is pretty fast， 他快地走 emphasizes the state of his walking， so you put the adv. 快地 in front of the verb 走 to modify the verb. But in oral Chinese, if you say that 他快地走, we can still understand you but quite weird, so you'd better say 他走得很快.

通常我们这样说：他走得很快。 不说：他快地走。 这里涉及到 “得” 和 “地” 的用法 得：动词+得+（副词）+形容词 例：他做得很好。 他说得很好。 他跑得很慢。 这种表达方式通常用来强调一件事情或一个动作做得怎么样。 地： 形容词+地+动词 例：慢慢地吃 轻轻地说 强调动作“吃”和‘说“的状态。 那我们看一下这两个句子：他吃得很慢。 （是带有一种评价的语气的） 他慢慢地吃。 （只是强调一种状态不带评价） 例如：我们在食堂一起吃饭，吃完了还要去逛街，我吃完了，你还在吃，那么就是我吃得很快，你吃得很慢。要是我等得不耐烦了，我还会说：”你吃得真慢！快点吃！“^_^ 要是我煮了一条好多刺的鱼，我会对小孩子说：”小心点儿，慢慢地吃。“于是你就能看到——他慢慢地吃。 要是我请你到我家吃饭，我先吃完了，我还会礼貌地对你说：慢慢吃！

er , for me I don't really say 他快地走. I think it's just a wrong sentence . that's the difference . wanna say he walk fast . 他走得快， sleep fast 睡得快, eat fast 吃得快。 by the way , 得 and 地。after a verb use 得 .like here , 走 a verb you need 得 but not 地。

'他走得快'means 'he walk fast'.Is usually used to describe his speed is fast. '他快地走' From the Chinese point of view, this is a syntax error in expression. so,他走得快‘is correct expression.