The invention provides an overload protection system for a construction lift. The construction lift is driven by a motor to run, the motor is controlled by a frequency converter, and the overload protection system comprises a curve creating unit, an analog quantity acquiring unit, a load capacity computing unit and an overload judging unit; the curve creating unit is used for creating an analog quantity signal and load capacity curve by means of weighing self-learning at a debugging state; the analog quantity acquiring unit is used for acquiring a current analog quantity signal from a weighing sensor; the load capacity computing unit is used for computing current load capacity corresponding to the current analog quantity signal by the aid of the analog quantity signal and load capacity curve; the overload judging unit is used for confirming an overload state of the construction lift when the certain current load capacity exceeds rated load capacity. The invention further provides an overload protection method for the construction lift. The overload protection system and the overload protection method have the advantages that the analog quantity signal and load capacity curve is created by means of weighing self-learning, and accordingly whether the construction lift is in the overload state or not can be accurately judged according to the load capacity computed according to the curve.