Aiming at the problem that the existing harmonic current detection algorithms are difficult to accurately detect subsynchronous harmonic current and supersynchronous harmonic current, an improved ip-iq harmonic current detection algorithm is proposed. Firstly, it is clear that the low pass filter gentle attenuation characteristics and insufficient dynamic adjustment ability are the fundamental reasons for the low harmonic current detection accuracy. Secondly, the low pass filter is replaced by a self-tuning filter with steep attenuation characteristics near the fundamental frequency. The self-tuning filter can enhance the detection effect of subsynchronous harmonic current and supersynchronous harmonic current without reducing the filtering effect of the integer harmonic current; The dynamic characteristics of ip-iq algorithm are ameliorated through the adaptive filtering algorithm based on the improved hyperbolic sinusoidal function. The adaptive filtering algorithm establishes the functional relationship between the step size parameter and the harmonic compensation current, and realizes the dynamic adjustment of the step size parameter. This algorithm overcomes the adverse influence of the time-varying quasi steady state characteristics of subsynchronous harmonic current and supersynchronous harmonic current on harmonic detection. In this paper, the detection effect of the improved algorithm is evaluated by current distortion rate and harmonic content rate. Simulation experiments verify the effectiveness of the improved algorithm. Compared with the traditional ip-iq harmonic current detection method, this method can improve the detection accuracy of harmonic current by 23.59%, and realize the accurate detection of harmonic current in the environment of subsynchronous harmonic and supersynchronous harmonic.