Abstract: In the dense complex signal radar environment, the estimation of the parameters Pulse Repetition Interval (PRI) and deinterleaving is a tedious problem. This paper presents a new method, named Square Sine Wave Interpolating Algorithm (SSWIA ) for deinterleaving based on a Time-Of-Arrival (TOA) analysis, which works well in the dense complex signal radar environment. The core of this method is that it turns the unequal interval TOA sequence into a continuous signal. Then the periodic TOA sequence in the mixed TOA sequence will be extract by using FFT, filtering and zero-cross detection technology. This algorithm is very successful in high-pulse-density radar environments and for complex signal types. The simulation results show that it has better precision of the estimation of parameter PRI, more quick speed of deinterleaving the mixed TOA sequence, less sensitive to interfering pulse, more robust to missed pulses than the conventional published techniques.