take part in指参加群众性活动、会议、劳动、游行等,往往指参加者持有积极的态度,起一份作用,有时与join in可互换.
例句：
①Will you take part in the English evening?
同我们一起参加英语晚会好吗?
②All the students took an active part in the thorough cleaning.所有的学生都积极参加了大扫除.
③We should take an active part in school activities.我们应该积极参加学校的活动.
join in通常指参加某种活动,尤其指和其他人一起参加某项活动.例句：
①May I join in the game?我可以参加这个比赛吗?
②I hope you”ll all join in the discussion.我希望你们大家都参加讨论.