考研失败可以用以下英文表达：
1. "Unfortunately, I did not pass the entrance examination."
2. "I was not successful in the postgraduate entrance examination."
3. "I failed the postgraduate entrance examination."
4. "I did not succeed in gaining admission to the graduate program."
这些表达都直接说明了考研失败的事实，可以根据具体语境选择合适的表达方式。