Abstract: As the cost caused by software vulnerabilities keeps increasing, people pay more and more attention to the researches on the vulnerability. Although discovering vulnerability is difficult because of the defect of vulnerability analysis, to predict the number of vulnerabilities is very useful in some domain, such as information security assessment. At present, the main methods to estimate the density of the vulnerabilities focus on the macro level, but they can not reflect the essential of vulnerability. A prediction model based on micro-parameter is proposed to predict the number of vulnerability with the micro-parameters of software, and it extracts the typical micro-parameters from some software series for the purpose of discovering the relationship between the vulnerability number and micro-parameters. With the hypothesis of vulnerability inheriting, the prediction model abstracts the micro-parameters from software and tries to find a linear relationship between the vulnerability number and some micro-parameters. This model also gives a method to predict the vulnerability number of software with its micro-parameters and the vulnerability number of its previous versions. This method is verified with 7 software series, and the results show the prediction model is effective.