A novel finite-difference time domain (FDTD) algorithm named equivalent circuit FDTD (EC-FDTD) is realized, which introduces lumped elements from transmission line theory into Yee cell. It includes lumped elements such as series inductance and shunt capacitance in the right-handed materials, as well as shunt inductance and series capacitance in the left-handed materials. Due to its promising physical thoughts, it can be easily generalized to arbitrary dispersive materials including frequency selective surfaces and metamaterials. The technology of streaming single-instruction multiple-data (SIMD) extensions (SSE) was proposed by Intel and is currently utilized in personal computers. SSE is a kind of parallel speedup technology in one core. The speedup can be achieved four times in principle without changing hardware. Combined with SSE, the EC-FDTD can be apparently accelerated. Twice speedup is achieved in the tests of this paper. The algorithm of EC-FDTD is utilized to design the wideband metamaterials absorbers by employing the single square and double square loops loaded with the lumped resistors. The invisible radome has a great impact on reducing the radar cross section of the antenna out of band. The radome is designed with operating frequency to be 1 GHz and the absent bandwidth from 3 GHz to 9 GHz by the algorithm. And then these prototypes are fabricated and measured. From the comparative results, the correctness of EC-FDTD and the speedup of the SSE are both verified.