We present a real-time fundamental current detection method under interharmonics and harmonics in power system based on high-resolution harmonics tracking algorithm (HRHTA) and fast sequential least square algorithm (FSLSA) for compensating interharmonics and harmonics simultaneously.The fundamental frequency of voltage is estimated accurately based on HRHTA firstly; then, the fundamental component of the corresponding current is extracted based on FSLSA. Besides, the stable computing method and the computation-parameter selection rules are proposed for HRHTA.The simulation results on the field interharmonics data show that the fundamental current can be extracted based on proposed method fast and accurately.There is hard algorithm stability and high frequency resolution on the HRHTA in fundamental frequency real time detecting of voltage with time varied interharmonics and noise. The proposed the computation selection methods and hard limit in fundamental frequency detection has been test valid. Based FSLSA to extract fundamental component the compensation energy is least in theory.