Abstract: In the case of unknown phase angle,the harmonic superposition calculation using the coefficient estimation method in the national standard is usually not ideal.According to the theory analysis of harmonic superposition,this paper develops a Monte Carlo method based on kernel estimate and important sampling to calculate the same-order harmonic current superposition of multiple harmonic sources.Firstly,the probability density function of harmonic current phase angle is calculated using the kernel density estimation and sampled by using the important sampling method to obtain the kernel sample data.Then,the Monte Carlo method and the kernel sample data are used to estimate the cross terms of harmonic superposition.Finally,the formula for harmonic current superposition is determined.Simulation analysis and actual examples show that the proposed algorithm can yield more accurate estimator of the superposition of harmonic current and be efficiently applied to the harmonic superposition of multiple harmonic source systems.