import requests
import time

headers = {
'user-agent': 'Mozilla/5.0 (Macintosh; Intel Mac OS X 10_13_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/76.0.3809.132 Safari/537.36',
'referer': 'http://movie.mtime.com/'
}
for num in range(1,4):
    params = {
    "tt": "{}".format(int(time.time() * 1000)),
    "movieId": "251525",
    "pageIndex": "{}".format(num), #为什么这个地方直接用num填进去会报错
    "pageSize": "50",
    "orderType": "1"
    }
    res = requests.get(
    'http://front-gateway.mtime.com/library/movie/comment.api',
    headers=headers,
    params=params)

    resJson = res.json()
    print("resJson:", resJson)
    if resJson:
        res = resJson['data']['list']
        for i in res:
            print('用户：', i['nickname'])
            print('评论：', i['content'])
            time.sleep(1)

改成这个，应该是res.json()的结果是None， 可能你的IP已经被封了，我这没事