An insulation resistance detection system for an electric vehicle to detect a positive insulation resistance between a positive electrode (200+) of a battery of the electric vehicle and an equipment grounding point, and detect a negative insulation resistance between a negative electrode (200-) of the battery and the equipment grounding point, characterized in that the insulation resistance detection system comprising: a negative detection circuit coupled to the battery in parallel, and comprising a first charge and discharge circuit and a first current-limiting resistor; the first current-limiting resistor coupled between the equipment grounding point and the negative electrode (200-); the first charge and discharge circuit comprising: a first charge circuit comprising: a first capacitor coupled between the positive electrode (200+) and the equipment grounding point, and a first switch coupled between the positive electrode (200+) and the first capacitor, and a first discharge circuit coupled to the first capacitor in parallel, a positive detection circuit coupled to the battery in parallel, and comprising a second charge and discharge circuit and a second current-limiting resistor; the second current-limiting resistor coupled between the equipment grounding point and the positive electrode (200+); the second charge and discharge circuit comprising: a second charge circuit comprising: a second capacitor coupled between the negative electrode (200-) and the equipment grounding point, and a second switch coupled between the negative electrode (200-) and the second capacitor, and a second discharge circuit coupled to the second capacitor in parallel, and a control unit configured to periodically turn on the first charge circuit to charge the first capacitor, periodically turn on the first discharge circuit to discharge the first capacitor, periodically turn on the second charge circuit to charge the second capacitor, and periodically turn on the second discharge circuit to discharge the second capacitor, wherein the first capacitor is charged to generate a first capacitor voltage, and the second capacitor is charged to generate a second capacitor voltage, wherein the first charge circuit and the second discharge circuit are simultaneously turned on, the second charge circuit and the first discharge circuit are simultaneously turned on, and the first charge circuit and the second charge circuit are not simultaneously turned on, wherein the control unit determines whether the negative insulation resistance is abnormal according to the first capacitor voltage and a battery voltage of the battery, and determines whether the positive insulation resistance is abnormal according to the second capacitor voltage and the battery voltage. a first charge circuit comprising: a first capacitor coupled between the positive electrode (200+) and the equipment grounding point, and a first switch coupled between the positive electrode (200+) and the first capacitor, and a first capacitor coupled between the positive electrode (200+) and the equipment grounding point, and a first switch coupled between the positive electrode (200+) and the first capacitor, and a first discharge circuit coupled to the first capacitor in parallel, a positive detection circuit coupled to the battery in parallel, and comprising a second charge and discharge circuit and a second current-limiting resistor; the second current-limiting resistor coupled between the equipment grounding point and the positive electrode (200+); the second charge and discharge circuit comprising: a second charge circuit comprising: a second capacitor coupled between the negative electrode (200-) and the equipment grounding point, and a second switch coupled between the negative electrode (200-) and the second capacitor, and a second capacitor coupled between the negative electrode (200-) and the equipment grounding point, and a second switch coupled between the negative electrode (200-) and the second capacitor, and a second discharge circuit coupled to the second capacitor in parallel, and a control unit configured to periodically turn on the first charge circuit to charge the first capacitor, periodically turn on the first discharge circuit to discharge the first capacitor, periodically turn on the second charge circuit to charge the second capacitor, and periodically turn on the second discharge circuit to discharge the second capacitor, wherein the first capacitor is charged to generate a first capacitor voltage, and the second capacitor is charged to generate a second capacitor voltage, wherein the first charge circuit and the second discharge circuit are simultaneously turned on, the second charge circuit and the first discharge circuit are simultaneously turned on, and the first charge circuit and the second charge circuit are not simultaneously turned on, wherein the control unit determines whether the negative insulation resistance is abnormal according to the first capacitor voltage and a battery voltage of the battery, and determines whether the positive insulation resistance is abnormal according to the second capacitor voltage and the battery voltage.