As more distributed new energy being accessed to power grid, it has a great influence on the harmonic studies of power system. It is urgent to solve the harmonic issues of distributed new energy connected to the grid and detect the harmonics and inter-harmonics accurately, figure out the distribution property of the harmonics, identify the harmonic sources and assess the harmonic responsibilities, as well as to reveal the mechanism of harmonic propagation and resonance and analyze the harmonic instability. Therefore, the harmonic hot issues of distributed generation connected to grid are described on aspects of harmonic measurement, harmonic identification, harmonic responsibility assessment, harmonic resonance and harmonic instability, which contribute theory reference to the studies on harmonic issues of distributed generation accessed to grid.