Network coding is an efficient way to reach the theoretical approximation of network capacity-transfer.This paper primarily studies the delay characteristic of data block under random network coding.Network coding is realitzed by MDS choosing Theorem and time delay forecast is built by gradient method.It is proved by emulating experiments that the smooth forecast value is approximate to the real value while the acute forecast value is bigger than real value

and block delay is a liner sale to block size

so is the channel utilization.