Active probe is the main method for Internet end-toend available bandwidth estimation. Based on the analysis of packet gap in active probing, an improved method to estimate available bandwidth is proposed, which is based on the concept of self-induced congestion. In this method, the transmission rates of probe packets are increased step by step and a new decision criteria, NWID (Normalized Weighted Increased Delay), is defined. Another idea is that sliding-window decision is adopted to obtain the available bandwidth in one measurement. Simulation and test results show that the measurement precision is improved with slightly adding probing overhead compared with pathChirp.