Abstract: To improve the accuracy of insulation detection between the high-power battery system and the chassis of electric vehicles under complicated working conditions, this paper builds a new insulation detection model. This model takes the battery internal resistances into consideration for insulation detection. Based on the proposed model, a Reliability Algorithm (RA) is developed. This algorithm realizes the reliability measurement of the detection dataset according to the change interval of the total voltage, and then selects a binary dataset that has the maximum reliability to calculate the system insulation resistance of the battery system. In order to restrain the random measurement noise, the moving average filter is applied to process the results. The experiments carried out the test platform of electric vehicles and the numerical simulation show that the internal resistance model and the reliability algorithm for insulation detection have good estimation accuracy and high robustness.