A test bench of steam condensation inside a long horizontal tube under vacuum condition was established. An experimental study was carried out to observe the influences of inlet mass flow rate

content of condensate and saturation temperature on the liquid level angle of the condensate when steam continuously condenses inside a horizontal tube. The correlation of liquid level angle is presented. It is found that

at a lower mass flow rate of steam

the liquid level angle of condensate increases with the content of condensate and the growth rate is fluctuated. At a higher steam flow rate

due to the influence of steam flow

the liquid level angle decreases and its edge becomes vague. The liquid level angle increases with the increment of saturated temperature or saturated pressure at the same flow rate of steam. The correlation of liquid level angle proposed in this paper can well predict the liquid level angle and liquid level of condensate in a horizontal pipe.