In　this　paper,　the　scale　ambiguity　in　underwater　monocular　visual　odometr　y　is　solved　with　2-D　sonar　measure-ments　obtained　from　three　viewpoints.　Each　measurement　value　is　formulated　as　geometrical　constraint　and　the　recovered　scale　can　be　expressed　in　closed-form.　Different　from　the　existin　g　method　which　assumes　the　features　being　on　the　same　plane　in　order　to　meet　the　pre-condition　of　quasi-homography　transformation,　ou　r　method　allow　s　the　observation　points　to　be　distributed　spatially　(not　limited　to　a　plane),　thus　extending　the　proposed　method　to　more　general　application　environments.　An　error　contribution　criterion　of　sonar　measurement　is　proposed　to　weight　the　constraints,　which　f　urther　reduces　the　influence　of　noisy　input.　Experiments　are　performed　in　both　simulated　and　real　environments.　For　nonplanar　case,　the　proposed　method　gives　improved　accuracy　after　employing　constraint　weighting.　As　for　planar　case,　ou　r　method　achieves　comparable　accuracy　to　the　existing　method,　while　the　time　consumption　is　much　lower.