First of all, the overview of the two is different:

1. diary overview: diary refers to the carrier used to record its contents. A diary also refers to a daily notebook or a record of things you encounter and do every day.

2. Composition summary: refers to the narrative method of expressing a theme through words after people's ideological consideration and language organization.

Second, the classification of the two is different:

1. Classification of diaries: Diaries can be divided into life diaries, work diaries, observation diaries, student diaries and compositions, as well as mood diaries and natural diaries.

2. Composition classification: Composition is divided into primary school composition, middle school composition and college composition (thesis). The genre of composition includes narrative, explanatory, practical and argumentative.

Third, the elements of the two are different:

1, the elements of a diary: a diary usually consists of two parts: the tail and the body. Diaries often record what they see, hear, do and think in the first person.

2. Elements of composition: time, place, people, cause, process and result of events (mostly narrative).

Baidu Encyclopedia-Diary (Narrative Practical Writing)

Baidu Encyclopedia-Composition (narrative method of expressing theme meaning through words)