An electrical connection defect detection system to detect whether an electrical connection between an under-test pin of an under-test device and a signal line of a circuit board is normal is provided. The electrical connection defect detection system comprises a signal provider providing a test signal to the under-test pin through the signal line, a detection module, an electrode board and a plurality of grounding paths. The electrode board comprises a detection surface to be adapted to a surface of the under-test device opposite to the under-test pin to make the detection module detect a capacitance value associated with the electrode board, the under-test pin and the signal line larger than a threshold value when their connection is normal. The grounding paths are connected to one of not-under-test pin groups respectively to further connect to the ground potential. An electrical connection defect detection method is disclosed herein as well.