To enhance the veracity of Izhikevich's neuronal model and plausibility of Izhikevich's neural network model, we revised Izhikevich's neuronal model, deleted neurons' synaptic connections to themselves and established the description of short-term depression and time delay along axon in Izhikevich's neural network model. The simulation results with the improved neuronal model show it is more efficient and accurate for computation, the improved neural network model spikes with less synchronicity.