Abstract: This paper analyzed the relations between the one way delay and the transmitting rate of packets. For the packet whose one way delay is the biggest, its transmitting rate almost equals to the available bandwidth. Based on this theory, a decreasing rate chirp algorithm (DRChirp) was proposed to measure the available bandwidth. Firstly, this algorithm searched the available upper bound of available bandwidth by using fast probe technology. Then, the exponential decreasing chirps were transmitted and the available bandwidth was calculated by means of the weighted average of the transmitting rates of packets with the biggest and the second biggest one way delay. The experiment results via NS2 simulator show that the proposed algorithm has higher accuracy than classic algorithm based on probe rate mode in multi hop networks.