Frequency domain optical imaging (OFDI) provides high resolution and sensitivity. However, the speed of the data processing program in C language limits its application. A real-time imaging system of OFDI based on field programmable gate arrays (FPGAs) is proposed. It adopts a high-speed digitizer board PXI14400 from Signatec for interferometric data acquisition. The acquired data is processed in the user defined FPGA on board in real-time with a pipeline data processing algorithm. The algorithm eliminates the complex conjugate ambiguity, overcomes the swept laser source's nonlinearity in k-space, and allows the data to be processed continuously. We also provide an economic method of IQ demodulation for FPGA data processing. The design breaks through the speed bottleneck of data processing, and allows the system to process each sample point at a frequency of 200 MHz.