如果心理素質是 "the capability of working under pressure" 的話，那應該就是 EQ or EI (情緒智商) 了 。 Emotional intelligence (EI) / Emotional Quotient (EQ) / Emotional Intelligence Quotient (E-IQ) refers to the ability to perceive, control and evaluate emotions. 一個人能夠控制自己的情緒，也就肯定可以 work under pressure 了。

Depends on what you're talking about - we can't translate from chinese directly of course :) I can say that in English, we typically don't use 'psychological' or any form of this word, it sounds much more formal, unlike 心裡, which is a very simple way to say it.. We usually only say "psychology" when referring to the science of psychology （心理學）. one good phrase comes to mind: "to see what someone is made of". "He is about to try something very difficult. We will find out what he is really made of". It means how strong his character is, what are his true capabilities.

It means: Psychological quality (Google Translate, 2012). :-)

心理素质 = psychological quality (in ideological education) http://www.mdbg.net/chindict/chindict.php?page=worddict&wdrst=0&wdqb=%E5%BF%83%E7%90%86%E7%B4%A0%E8%B4%A8