Abstract: The traditional blade tip timing (BTT) technique cannot monitor the blade vibration information effectively under the condition of variable speed. In order to solve this problem, a new blade vibration monitoring method based on multi-phase at variable speed was proposed in this paper. In this method, interphase reference points are arranged evenly on the rotating shaft to estimate the rotation speed accurately. In the meantime, some virtual reference points are inserted between these multi-phase according to the number of involved blades, and they are used as markers to measure blade vibration at variable speed. This method is also applicable to the measurement of blade vibration at constant rotation speed. Then, the formula of blade vibration measurement at variable rotation speed was deduced based on this method. Finally, the feasibility and applicability of this method were verified by means of numerical modeling and experimental simulation. It is shown that the average relative measurement error of this multi-phase based vibration monitoring method for rotating blade at variable speed is lower than 7% while that of the traditional method is above 200%. Obviously, this new method breaks through the technical bottleneck of BTT technique which cannot monitor the blade vibration at variable speed.