需要先安装python-docx:

pip install python-docx

再使用以下的代码：

import docx
from docx.shared import Cm


def replace_img(in_word_path, out_word_path, output_paragraph_idx, new_img_path, height, width):
    """ Replace a image in a docx(Word) file. :param in_word_path: The path of the input docx file to be replaced :param out_word_path: The path of the output docx file :param new_img_path: The path of the image that will be the new image in the docx file(i.e. one image(The image is assigned by output_paragraph_idx) will be replaced by the image which is in img_path) :param output_paragraph_idx: The paragraph index of the image in the docx file(The index starts with 0) :param height: The height of the new image which is in centimeters. :param width: The width of the new image which is in centimeters.. :return: Empty """
    doc = docx.Document(in_word_path)
    para = doc.paragraphs[output_paragraph_idx]
    para.clear()
    pic = para.add_run().add_picture(new_img_path)
    pic.height = Cm(height)
    pic.width = Cm(width)
    doc.save(out_word_path)

如果有错误，欢迎指正。