Some issues such as CRL/OCSP (Certificate Revocation List / Online Certificate Status Protocol) unavailable, previsioned trust anchor unavailable, high communication load arise when PKI (Public Key Infrastructure) is leveraged into mobile networks. A blockchain based PKI framework in mobile network is proposed to solve these issues. The system is constituted by submission nodes, validator nodes, inquiry nodes. Scenarios and application cases are provided, and it shows the system can be widely used in mobile networks. The blockchain based PKI system is analyzed and compared to traditional solutions. It shows the trustworthy of SSL (Security Socket Layer) certificates and device certificates are the same as those in traditional PKI system. The storage requirement and certificate capacity of blockchain based PKI system is analyzed. Since certificates have expiry dates, the optimization method based on the invalid certificates is proposed. The optimization improves the storage efficiency of the blockchain based PKI certificate management system.