表示“在聚会上”“在晚会上”，一般是用 at the party 吧！如：
I enjoyed myself at the party. 这次聚会我非常快活。
He behaved foolishly at the party. 他在聚会上举止愚蠢。
Did you see them at the party? 在晚会上你见到他们了吗?
His appearance at the party was very welcome. 晚会上他的出现遭到了欢迎。
但看到如此一个句子：
We had a cosplayy chat in the party. 大家在聚会上进行了亲密的闲谈。
这里用了 in the party——如此用也是对的吗？
▲表示“在聚会上”“在晚会上”等，一般用介词 at。更多例句如：
Who else was at the party? 聚会上还有哪个?
He enjoyed himself at the party. 他在聚会上很愉快。
Were there many people at the party? 聚会上的人多吗?
He finds it hard to mix at parties. 他感到非常难在聚会上与人攀谈。
Guess who I saw at the party yesterday? 你猜我昨天在聚会上遇到哪个了?
I am glad that you had a good time at the party. 我真开心你在晚会上玩得高兴。
▲但《英语常用词使用方法解析大词典》觉得用 in the party 是错的，也有点过于绝对。其实用 in the party 也是可能的，只不过不如用 at the party 一般而已。如以下各例句均摘自词典或语法著作：
The mood in the party was joyful. 聚会上的氛围是让人愉快的。（《朗文英语联想活用词典》）
John will sing in the party and Mary won’t. 约翰会在晚会上唱歌，但玛丽不会唱。（章振邦《新编英语语法》）
Each girl in the party was paired off with a boy. 晚会上每一个女生都与一个男生配成一对。（张道真《现代英语使用方法词典》）
▲顺便补充一句：用 in the party 表示“在党内”，则是非常一般的使用方法。如：
She was active as a left-winger in the party. 她是党内积极的左翼分子。
The accusations caused a split in the party. 这类指控使党内出现分裂。
There have been deep divisions in the party over Europe. 该党内对欧盟问题存在紧急分歧。
He had the unhappy knack of making enemies in the party. 他一直在党内树敌，弄得非常不愉快。
He had manoeuvred his way into a position of strength in the party. 他设法在党内获得了实权地位。
