This paper presents an FPGA based implementation for adding White Gaussian Noise (WGN).By using matrix transformation and XOR operation, uniformly distributed random numbers (UDRN) could be easily generated.Then we used look-up table to convert the UDRN into Gaussian Random Number (GRN) based on Box-Muller method.After GRN was generated, an automatic searching and approaching method was used to add certain White Gaussian Noise on a zero-IF signal to match a SNR demand.Results of simulations and experiments show that the device can be used to add White Gaussian Noise on signals of wireless communication systems.