Concerning the problem that the current research on password semantics is mainly based on English datasets and restricted to some units like common words or surnames, by using data analysis technology based on password strings, a Chinese context password analysis method based on known-password elements was proposed with the pattern library based on Chinese poems and idioms in Chinese context. Firstly, the known-password element was identified. Then, it was considered as a single password degree of freedom. Finally, the freedom attack cost within a given attack success rate was calculated and the quantitative security of password was obtained. After quantitative analysis of large amounts of plaintext passwords by designed experiments, it is concluded that 80% of user passwords are low secure and can be easily broken by dictionary attacks in Chinese context.