In this paper, seawater with simple pretreatment and seawater with softening pretreatment were used to horizontal tube falling film evaporation experiments respectively. Experimental results showed that these two heat-transfer coefficients gradually increased with boiling point ,and the heat-transfer coefficient of seawater with softening pretreatment was slightly higher than seawater’s when the boiling point was below 70℃; The heat-transfer coefficient of seawater with softening pretreatment was much higher than the seawater’s when the boiling point was above 70 ℃. In a word, seawater with softening pretreatment could achieve high heat-transfer coefficient at high temperatures. The experiment provided the experimental and designed base for the combination of softening pretreatment and multiple effect evaporation system.