Lag synchronization of spatiotemporal chaos in a weighted network with ring connection is studied in this paper. Spatiotemporal chaos systems are taken as the nodes of the network，and connections between the nodes are made through a weighted ring. According to stability theory，the condition to realize lag synchronization of the network is obtained by identifying the maximum Lyapunov exponent of the network. Lag synchronization exists in the whole network when the largest Lyapunov exponent is less than zero，and the coupling strength between the nodes can be given any weight value. Autocatalytic reaction-diffusion chaotic systems are taken as the nodes of the network，and simulation results show the effectiveness of the method.