Softening, namely degradation, is an important characteristic for the components long-termly operating in high temperature environment. In this article, hardness is adopted to indicate this effect. In order to study the independent effect of high temperature and stress on the material properties, the zero-stress ageing experiments at 540 oC, 565 oC, 660 oC and the stress-accelerating softening experiments (i.e. creep experiment) at 540 oC, 565 oC with interruption were carried out in steel 30Cr1Mo1V, respectively. The stress range tested was from 240MPa to 320MPa. The Vicker’s hardness was measured. The relationship between Larson-Miller parameter and the Vicker’s hardness under zero-stress softening condition and under stress-accelerating softening condition is obtained. Based on the extraction of the effects of temperature and time, the stress softening effect formulae are established.