To design a low-calculation and high-precision TOA estimation algorithm for IR-UWB ranging systems, a two-step TOA estimation method which jointly employs energy-detection (ED) and matchfiltering (MF) is proposed. Based on analyzing the principles of the two-step method, it was pointed out that the success rate of DP block detection in the first step and the setting of MF-threshold-factor in the second step were the key issues that affect the performance of the method. Algorithm selection of the first step and setting of the energy integration interval, which are the two factors that affects the success rate of DP block detection, were discussed through simulations. The idea of DMR (DP to minimum energy sample ratio) based MF-threshold-factor selection was proposed. Results show that the proposed two-step method greatly outperforms the one-step energydetection based non-coherent method, while largely decreases the computational complexity compared to the one-step match-filtering based coherent method.