The three phase unbalance of low voltage distribution network has become a common problem of widespread concern. Analysis, evaluation and management need accurate algorithms to ensure. In order to understand the error produced by unbalanced estimation algorithm in three-phase unbalanced system, the influence of phase angle variation of current sequence components on the algorithm of three kinds of current imbalance is studied, and then a most effective and least error estimation method is chosen. This paper first introduces several algorithms of voltage and current unbalance in standard, theoretically deduces the cause of unbalanced voltage, and gives several calculation methods of unbalanced current. On this basis, the factors that affect the estimation methods of three kinds of current imbalances are studied by MATLAB simulation experiments, and some feasible suggestions are put forward. In the end, the above conclusion is verified by the analysis of the measured data. In this paper, the research of four kinds of current imbalance estimation algorithm has great guiding significance for engineering practice, and it can provide some reference for the treatment and compensation of three-phase unbalanced system.