Resistive random access memory (RRAM) has attracted considerable interest for next-generation non-volatile memory due to its fast switching speed, high storage density and excellent scalability. To effectively control the switching characteristic with excellent memory performance, a complete study of the switching behavior is essential. In this work, we utilize SrCoOx (SCO) which grows on Nb-doped SrTiO3 (Nb-STO) substrate as our dielectric layer since it exhibits large different resistance between SrCoO2.5 and SrCoO3-��, where the value of SrCoO2.5 is higher than that of SrCoO3-��. Based on this characteristic, we fabricated a Au/SCO/Nb-STO device, and measured the SET (~1.6 V) and RESET (~-5.3 V) process with more than 700 cycles. Meanwhile, the conducting filaments were observed via in-situ transmission electron microscope (TEM). From the HRTEM results and corresponding FFT-DP (Fast-Fourier-Transform Diffraction pattern), it is clearly demonstrated the formation of conducting filaments is from SrCoO2.5 to SrCoO3-��. Accordingly, the formation/rupture of conducting path is due to the movement of oxygen vacancy, and hence its resistance is able to switch reversibly between low resistance state and high resistance state. This study not only revealed the switching mechanism of SrCoOx but also proved it to be the promising candidate for RRAM application.