The invention provides an undersampled leaf apex timing vibration signal reconstruction method and a device thereof. The method comprises the steps of (1) acquiring the displacement sampling data of a non-uniform blade end based on a blade end timing vibration measurement system; (2) determining the vibration characteristics of a high-speed blade and the frequency band range of the high-speed blade; (3) based on the periodic non-uniform sampling theory, completing the interpolation reconstruction for the vibration signal of the blade. The vibration displacement is acquired by a first blade end timing sensor and a second blade end timing sensor, wherein the first blade end timing sensor and the second blade end timing sensor are arranged in a casing. Based on the method, reconstructed signals are agonic and non-biased. Meanwhile, only by means of two blade end timing sensors, corresponding data can be acquired. In this way, not only data can be acquired completely and accurately, but also the cost is effectively reduced.