三年级下册英语中描述人物的句子可以包括外貌特征、性格特点以及行为表现等方面。以下是一些例子：

1. She has a round face with a pair of round eyes, a little flat nose, and a big mouth. She is my best friend and YanWenYi Chen Weijun.

2. She is a very good classmate. She learns seriously, loves reading, and is helpful at home.

3. Her strengths are her serious learning attitude and love for reading, but her weakness is strong jealousy.

4. She has a pair of watery little eyes, a cherry red little mouth, and a small nose. Her cheeks are full and her skin is white and rosy. She is loved by everyone.

5. He is a handsome fellow with straight strong limbs, not too large, tall, and well-shaped.

6. His eyes are as pure as spring water, containing a soft light.

7. Mike is an American. He is a lively and cheerful child who likes sports and playing.

8. Chenjie is a Chinese. She is a smart and diligent child who likes studying and reading.

9. Wuyifan is a Chinese. He is a friendly and kind child who likes to help others.

这些句子可以帮助你描述三年级下册英语中的人物形象。根据具体需要，可以选择合适的句子或进行适当的修改来适应不同的描述场景。