Abstract: In this study, cracks were prefabricated in cubic sandstone specimens to investigate the precursor characteristics of fractured rocks under different stress conditions. Two forms of parallel and collinear cracks were made to represent different rock structural planes. Biaxial compression tests were conducted on prefabricated fractured sandstone under lateral pressures of 0, 5, and 10 MPa, respectively. Acoustic emission and digital imaging technologies were used to monitor the development of internal fractures and surface deformations of the rock. The development and process of rock fractures were studied using the acoustic emission event rate function and maximum principal strain field variation of sandstone. The results showed that sandstone exhibited progressive failure characteristics. The failure mode is mostly dominated by splitting failure, accompanied by compression shear failure, and the failure mode often presents a skewed “I” shape in the direction of the maximum principal stress, occasionally having an “X” shape. The confining pressure has a “reinforcing” effect on the strength of the rock, and as the confining pressure increases, the “reinforcing” effect becomes more significant; however, simultaneously, the stepwise trend of progressive rock failure decreases. In addition, a strong correlation exists between the acoustic emission event rate function and the variation of the principal strain field on the rock surface, and their joint analysis can effectively characterize the failure process of rocks. In the compaction stage, the acoustic emission event rate is extremely low. During the elastic and plastic stages, the acoustic emission event rate gradually increases and remains high. Notably, the primary strain field shows a trend of localization. In the failure stage, a localized band of the primary strain field is formed, and the acoustic emission event rate gradually and violently fluctuates. Along with the rapid development of rock fractures, the acoustic emission event rate suddenly increases. To characterize the precursor information of the sample, the coefficient variation (CV) and standard deviation (SD) of the longitudinal strain field were introduced to describe the precursor information of the digital image before rock failure, and the acoustic emission precursor information before rock failure was described using the acoustic emission ring count. Using the entropy weight method, the weights of the acoustic emission precursor and digital image strain precursor indices were determined, and a fusion index Acoustic emission and DIC (AD) that reflects the internal and surface information of the rock was obtained. The results showed that the fusion index does not have an advantage in warning time compared to the acoustic emission ringing count, longitudinal displacement field variation coefficient, and longitudinal displacement field variation SD, but exhibits more notable precursor characteristics under uniaxial loading. However, under biaxial loading, it has an advantage in warning time and exhibits more significant precursor characteristics. In engineering rock masses, rock failure is mostly in a state of biaxial stress. The findings of this study provide a reference for the selection of precursor parameters for engineering rock mass failure.