Wireless sensor network is remarkable for its promising use on human-unattended information collection, such as forest fire monitoring.??In order to support efficient communication, many routing algorithms specially designed for such networks have been proposed. However, there is no idea about whether these proposed routing algorithms are already good enough or still have a long way to become “perfect”, since there is currently a lack of understanding about the optimal routing performance. This paper makes a progress in the understanding of the optimal routing performance. Metrics here used to measure the routing performance are the network lifetime finally acquired and the total information finally collected. The condition used to judge the network’s death is defined by the user’s requirement on the guaranteed network information collecting ability. Optimization models based on the metrics and death condition mentioned above are proposed. Experiments show some existing routing proposals already work well when the user’s requirement is strict, but few of them satisfy when the user’s requirement is loose.