DateTimeField's timezone changed after serializing

[Rnine-99]

the following picture shows the DateTimeField in a instance before and after serializing. could anyone tell me why it changes?

this is model reply:

class Reply(models.Model):
    topic = models.ForeignKey(Topic, verbose_name=u"话题", on_delete=models.CASCADE)
    replier = models.ForeignKey(User, verbose_name="回复人", on_delete=models.CASCADE)
    content = models.TextField(verbose_name=u"回复内容", default="")
    releaseTime = models.DateTimeField(default=datetime.now, verbose_name=u'发布时间')

this is serializer:

class Reply_serialize(serializers.ModelSerializer):
    replier = serializers.SerializerMethodField()
    # releaseTime = serializers.DateTimeField(format='%Y-%m-%d %H:%M:%S')

    class Meta:
        model = Reply
        fields = "__all__"

    def get_replier(self, new):
        attrs = new.replier
        return [{"replier_id": attrs.id, "replier_name": attrs.username}]