This paper designed a 1-Mb HfOx-based embedded Resistive Random Access Memory (RRAM) device with a one-transistor-one-resistor (1T1R) structure, and systematically investigated its working temperature range. It noted that this embedded RRAM macro has a 1.6X working temperature range than previous design for some extreme environment. Using the peripheral-assisted technique, it can enable the error rate of the RRAM macro under 0.5% which can reduce the complexity of ECC function. Experimental results show that, the RRAM macro achieves a wider work temperature range (between −55°C and 150°C), which improves the reliability of the entire embedded RRAM macro and has a high robustness as well.