To keep something in check 意思是约束，控制某事。

Keep emotions in check就是不显露感情。

例句：

美国乔治华盛顿大学的研究人员说，A 15-minute walk three times a day after meals helpspeople in their 70s and 80s to keep their blood sugar levels in check. 每天三次饭后走15分钟，有利于七八十岁的人控制血糖水平。

Bank Indonesia's newGovernor said that keeping inflation in check would be one of the centralbank's top priorities. 印尼央行新行长说，控制通货膨胀将是央行的工作重点之一。

We must keep our spending in check this month．我们必须控制这个月的开销。

Unless imports are kept incheck we are in danger of losing our favourablebalance of trade．如果不控制进口，我们就有失去贸易有利平衡的危险。

If I hadn't kept myselfin check，I might have saidsomething that I would have regretted later．如果我不控制自己的话，我就会说出一些以后要后悔的话。