If I didn't have a Shenzhen hukou, I got more than 600 points in the senior high school entrance examination in Shenzhen. Can you be admitted to a key high school?

You can go to Shenzhen for high school from other places. Whether your score is higher than the average score of key high schools depends on whether it is higher than the average score of key high schools. If it is around 650, it will definitely be accepted, but whether you can directly take the college entrance examination in Shenzhen depends on the regulations of the Shenzhen Admissions Office:

According to the current college entrance examination registration policy, Shenzhen household registration candidates refer to those who have obtained Yin Hong household registration in Shenzhen. Blue-printed hukou cannot be used as the basis for applying in Shenzhen. All high school graduates who have registered in Guangdong province and have studied in Shenzhen for three years in high school must, in principle, return to their registered residence. If you need to borrow a test in our city, you need to provide the original household registration book of the whole family (including parents or guardians) in Guangdong Province, relevant certification materials and temporary residence permits within the validity period before you can apply.

The Municipal Admissions Office will strictly examine candidates' applications for borrowing exams. Candidates who practise fraud or have incomplete materials or are suspected of being "immigrants in the college entrance examination" will be reported to their superiors for strict investigation. If they are found, their qualifications for entering the exam or admission will be cancelled, and those who have already enrolled will be disqualified and the relevant personnel will be held accountable. In addition, according to the regulations of Guangdong Province, candidates with household registration in other provinces are not allowed to borrow exams in Guangdong Province.