An innovative nondestructive measurement method of Al alloy surface strengthening layer depth using frequency sweep eddy current testing (SFECT) technology is proposed. Based on the analysis of the forming mechanism of Al alloy surface strengthening layer and the comparison of several possible detection methods, the applicability of SFECT method is discussed theoretically. By means of electromagnetic simulation software Ansoft Maxwell and orthogonal experimental design method, the SFECT coil model is built. The optimal design and simulation of the parameters of the SFECT coil are carried out, and optimal coil structure parameters and lift-off height are obtained. Simulation of depth detection of Al alloy surface strengthened layer using SFECT coil is implemented, and then preliminary experiment of Al alloy surface strengthening layer depth measurement with the self-fabricated SFECT coil is completed. The simulation and experiment results show that SFECT method can be applicable for nondestructive testing of Al alloy surface strengthening layer depth.