Abstract: At p=3-10MPa, G=300-600kg/（m²·s）, Δt_sub=30-90℃, and q=0-190kW/m², the experiments on steam-water two-phase flow instabilities have been performed. The test sections are parallel inclined internally ribbed pipes with an outer diameter ofφ38.1mm, a wall thinkness of 7.5mm, a obliquity of 19.5o and a length more than 15m length. Based on the experimental results, the effects of pressure, mass velocity, inlet subcooling and asymmetrical heat flux on steam-water two-phase flow density wave oscillation were analyzed. The experimental results showed that the flow system were more stable as pressure increased. As an increase in mass velocity, critical heat flux increased but critical steam quality decreased. Inlet subcooling had a monotone effect on density wave oscillation, when inlet subcooling decreased, critical heat flux decreased. Under a certain working condition, critical heat flux on asymmetrically heating parallel pipes is higher than that on symmetrically heating parallel pipes, that means the system withl symmetrically heating parallel pips was more stable.