Abstract In-situ stress is the key parameter for underground and slope rock engineering design optimization. Hydraulic fracturing method and trepanning stress relieving method are the two main in-situ stress measurement methods for the present, but both of the two methods have some disadvantages such as strict operating conditions, complicated operations, high cost, etc. which have not been overcome till now. With a case of high-steep open pit slope, the paper begins with hydraulic fracturing method to measure the in-situ stress and then, on this basis, based on plane stress condition, the paper adopts acoustic emission method to measure the horizontal maximum principle stress and its direction. It indicates that the test results of acoustic emission are consistent with that of hydraulic fracturing method.