bobbin thread太松，你把spool thread调再松也没用啊。你要调节bobbin tension.还有，你先检查你底线thread的对不对，该卡的地方卡住了没有，方向对不对。重新thread一次，严格按照说明书。如果thread没问题，底线还是这样， 再调节bobbin tension.
[url=https://help.brother-usa.com/app/answers/detail/a_id/70520/~/adjust-bobbin-tension]https://help.brother-usa.com/app/answers/detail/a_id/70520/~/adjust-bobbin-tension[/url]
[url=https://help.brother-usa.com/app/answers/detail/a_id/70520/~/adjust-bobbin-tension]https://help.brother-usa.com/app/answers/detail/a_id/70520/~/adjust-bobbin-tension[/url]