Secret image sharing is a method to transmit and store an image safely. The security of secret image sharing is based on the fact that the values are operated in the finite field and the number of pixels is high enough to ensure security. However, the time complexity to encode and decode a secret image is not acceptable in real-time application. There are some papers discussing how to upgrade the efficiency of encoding phase while few papers exploring how to decrease the decoding phase time. This paper proposes a method to achieve to speed up decoding phase by parallel processing.