1. 两者都可表示过去反复发生的动作。如：
In those days he would help her with her gardening. 那时他常来帮助她种植花木。
I used to write poetry when I was your age. 我像你那么大时常常写诗。
I don’t swim as often as I used to. 我游泳的时候不像过去那样多了
Children are not so well-behaved nowadays as they used to be. 孩子们现在没有过去那样听话了。
有时两者可互换。如：
When we were children we would (used to) to skating every winter. 我们小时候，每年冬天都支溜冰。
2. 但在下列情况中一般只用used to, 而不用would：
(1) 用来表示过去与现在的对比，即“以前这样，但现在不这样了”。如：
I used to go on Saturdays, but now I no longer do so. 过去我星期六经常去但现在我不去了。
(2) 表示过去持续的状态。如：
He used to like you. 我原来喜欢你。
There used to be a tree here. 原来这里有棵树。