I am assuming that you'd like to know the difference between 我一个人 and 我自己，or 我一个人的 and 我自己的。 they're interchangeable in most of the cases. I did it by myself=我一个人做的=我自己做的. In some contexts, 我一个人 would be used to put more emphasis on the fact that it was me and not anyone else. anyway the difference is subtle but still noticeable in some situations. 这是我一个人的房子： （it implies that you are single and buying solo, you have that house in sole ownership, which means you are the only title holder. ） 这是我自己的房子：（it implies that this is my house instead of a rental house. it doesn't matter weather or not a couple own a property together.） If you said these two sentences above to your partner, they would mean exactly the same thing; in which situation you two were probably negotiating a divorce settlement.