Attend here means to be at a certain place at a certain time. Participate here means to get involved in or to share in a specific activity, So it depends on what you are trying to emphasise I cannot attend the lesson as I have medical appointment I cannot participate in the class because there are no other students in the class today.

The meanings are different. 'Attend' means to be present. 'Participate' means to take an active part. It is, of course, possible to attend without participating. If you have sat in the classroom for the entire lesson without saying a word, you have attended the lesson but not really participated. If a teacher says in a report that a student doesn't attend classes enough, this means that they are absent too often. If the teacher says that the student doesn't participate, this is nothing to do with attendance - it means that the student is too passive, and doesn't get involved in the lessons enough. If your sentence is a message to say that you simply won't be at the lesson, then 'attend' is the better word here.

in this case it seems more likely to choose the first one, usually the word"attend" uses for classes and be in the specific area or place and situation ,so i think the first one is better

One would normally use "attend". Of course, the best learning involves some participation, in which case "participate" might be appropriate.