Due to the increasing demand for high-throughput and low-cost mobile devices, design of high-parallel reconfigurable FFT processors has become more and more important. However, FFT lengths varied, designing a multi-length FFT processor with the requirement meet has become unprecedentedly challenging, especially as the FFT lengths includes non-power-of-two. In this paper, reconfigurable mixed-radix 2k×3-point feedforward FFT architectures are proposed. It can be realized as any power-of-two parallelism to achieve the sweet spot, with performs high enough to meet the requirement and still promise a reasonable cost. A proposed feedforward radix-3 FFT is applied in the architecture, empowering the FFT processor to achieve high parallelisms. An 8-parallel 128-2048/1536-point FFT processor for the 4G LTE system is implemented with TSMC 90nm technology. Compared to the existing designs, this work offers a high-throughput and high area-efficiency solution for mixed-radix FFT operation.