考研英语中常用的成语包括但不限于以下几个：
1. 爱屋及乌 - Love me, love my dog.
2. 百闻不如一见 - Seeing is believing.
3. 比上不足比下有余 - Worse off than some, better off than many.
4. 谁言寸草心报得三春晖 - Such kindness of warm sun, can't be returned.
5. 人生苦短，学艺无穷 - Art is long, life is short.
6. 三思而后行 - Look before you leap.
7. 有其父必有其子 - Like father, like son.
8. 先入为主 - First impressions are firmly entrenched.
9. 跑得了和尚，跑不了庙 - Even if the monk can run away, his temple cannot run with him.
10. 打死我也不说 - Even if I were to be beaten to death, I will not tell.
11. 谦虚使人进步，骄傲使人落后 - Modesty helps one go forward, whereas conceit makes one lag behind.
这些成语可以帮助考生更好地理解和表达英语，提高阅读理解能力和写作水平。