"He gets up at six o'clock in the morning" 是表示他早上六点起床的正确英语表达方式。
其中，"gets up" 是 "rise" 的过去式，意思是 "rise from a lying, sitting, or kneepng posture"，表示"站起来"。
"at six o'clock" 是时间状语，表示"在六点"。
"in the morning" 是时间状语，表示"在早晨"。
例句：
He gets up at six o'clock in the morning to exercise. 他早上六点起床做锻炼。
I always wake up early, I get up at six o'clock in the morning. 我总是早起，早上六点起床。
She has to get up at six o'clock in the morning for work. 她必须早上六点起床去上班。