拒绝邀请的英语作文通常遵循以下结构：

开头

对邀请表示感谢。

简短地提及收到邀请并对此表示荣幸。

中间

具体说明无法参加邀请的原因。

可以包括时间冲突、已有安排、健康问题等。

表达对于无法出席的遗憾之情。

结尾

对主办方表示感谢，并祝愿活动顺利进行。

如果可能，可以提出替代方案或推荐其他人参加。

```

Dear [Name],

I hope this letter finds you in good health and high spirits. I am writing to respond to your kind invitation to [event/occasion] on [date]. I would like to express my gratitude for considering me and extending such a gracious invite. However, after careful consideration, I regret that I cannot accept your generous invitation.

The reason for my decline is that I have a prior commitment on the same day as the event. This commitment has been in place for quite some time and holds significant importance for me. I hope you can understand my position and excuse my absence. I truly value the opportunity to meet and engage with you and others at the event and regret that I will not be able to attend.

Thank you once again for your invitation. I wish you all the best and hope that the event goes smoothly. Please feel free to reach out to me if there is anything else I can do to assist or if you would like to discuss alternative arrangements.

Sincerely,

[Your Name]

```

请根据实际情况调整上述模板中的内容，以确保信件既真诚又符合具体情境。