Packet sampling measurement is a key technique in high-speed network traffic monitoring and management. In this paper, packet sampling techniques are introduced and analyzed after the presentation of related background researches. Then time-trigger and event-trigger Poisson sampling techniques are evaluated separately on several aspects such as packet length distribution, average packet length and the comparison between sampled volume and the whole traffic volume. The experiment results support that event-trigger Poisson sampling technique shows better performance than time-trigger Poisson sampling technique. At last, a heuristic explanation is briefly discussed and the prospect of packet sampling is depicted.