两者均可表示“宣布”，区别如下：
1. announce 主要指宣布大家期待的或与大家有关的事情，所涉及的情况通常是别人原来不知道的事，含有预告的意思。如：
The date of his visit has not been announced. 他来访的日期尚未公布。
They announced their engagement to the family. 他们向家里宣布他们已经订婚了。
2. declare 含有庄严宣告或交代清楚的意思，所涉及的事情不一定是别人不知道的。如：
He was declared to be guilty. 他被宣判有罪。
Bulgaria declared her independence in 1908. 保加利亚于 1908 年宣布独立。
1 【Declare】 , 【announce】 , 【publish】 , 【advertise】 , 【proclaim】 , 【promulgate】 , 【broadcast】 (and their corresponding nouns declaration, announcement, publication, advertisement, proclamation, promulgation, broadcasting) denote to make known (or a making known) openly or publicly.
To 【declare】 is to make known explicitly or plainly and usually in a formal manner.
To 【announce】 is to 【declare】 especially for the first time something presumed to be of interest or intended to satisfy curiosity.
To 【publish】 is to make public especially through the medium of print.
To 【advertise】 is to call public attention to by repeated or widely circulated statements. In its general sense it often connotes unpleasant publicity or extravagance in statement.
In its specific sense, as implying publicity for the sake of gaining patronage or support for an article of merchandise, it implies the use of communication media (as the press, the radio, handbills, or billboards); so used, it is devoid of unfavorable connotation.
To 【proclaim】 is to 【announce】 orally, sometimes by means of other sound (as of a trumpet), and loudly in a public place; by extension, to give wide publicity to, often insistently, proudly, boldly, or defiantly.
To 【promulgate】 is to make known to all concerned something that has binding force (as a law of the realm or a dogma of the church) or something for which adherents are sought (as a theory or doctrine).
To 【broadcast】 is to make known (as by radio or television) in all directions over a large area.
