There are multiple mutation points in the acoustic emission （AE） cumulative curve in the Kaiser experiments of reservoir cores， causing the routine Kaiser effect point discriminant method to be inaccurate， and there is even a problem that the Kaiser point cannot be read. To solve this problem， an optimized Kaiser effect point discriminant method combining AE energy spectrum and cumulative AE curve is proposed in this paper and applied to the prediction of reservoir in-situ stress in Block X of an Oilfield.The experimental results of core uniaxial loading show that at the initial period of core loading， the core is in the compression stage， with a large number of AE and a wide fluctuation range of AE energy values. In the middle period of loading，the core is in the elastic deformation stage. The amount of AE is small， and the AE energy value is low. The range of change is uniform. At the late loading period， the stress reaches the fracture pressure of the reservoir core， and the core ruptures. The number of AE increases sharply， and the AE energy value reaches a peak. In the middle period of loading， the core suddenly releases a large amount of energy，and the AE number and energy value have a sudden increase， followed by a rapid decrease when the axial stress reaches the historical maximum stress of the reservoir core. This phenomenon is in accordance with that of Kaiser. Therefore， the Kaiser effect point can be determined by combining the AE energy spectrum and cumulative AE curve. By using the optimized Kaiser effect point discriminant method， the in-situ stress distribution in Block X of an Oilfield is analyzed， and the results are in good agreement with the field test results.