Dual-satellite Time-Difference of Arrival (TDoA) and Frequency-Difference of Arrival (FDoA) positionings utilize just two satellites to locate the emitter, bearing lower cost and difficulty than multi-satellite positioning, and better real-time performance than single-satellite positioning system, more suitable for practical applications. In order to solve the nonlinear optimization problem in the process of solving the TDoA/FDoA equation, an Improved Particle Swarm Optimization (IPSO) algorithm is put forward. Dual-satellite TDoA/FDoA location systems use Newton method with high precision, but there exists unsolvable blind areas of initial value of iteration. To address this issue, an cascaded localization method of IPSO and Newton iteration is proposed, in which the IPSO algorithm gives coarse localization result with rapid speed and reliable convergence, and this coarse result is used as the initial value of Newton iteration, so as to reduce the positioning error and avoid non-convergence. By analyzing the simulation results, the proposed algorithm not only increases the success rate of effective initial point selection by 48.15% compared to the Newton method, but also cuts the computation and improves the computational speed.