The utility model discloses a measure long instrument of coral branch for it is long to measure the coral branch, which comprises an outer shell, be provided with the electron protractor in the shell,connect the telescopic to survey long ruler on two gage beams of electron protractor respectively, it is parallel with the gage beam to survey long ruler, survey long ruler stretches out from the continuous arc wall of shell lateral wall, the shell surface is equipped with the demonstration pane corresponding to the data display screen position of electronics protractor, the shell surface is equipped with long display screen of branch and data input module, be equipped with waterproof cavity in the shell, be provided with calculation module in the waterproof cavity, calculation module and thelong display screen of branch, the equal electrical property of data input module links to each other. The utility model discloses by surveying two length of sides that long ruler measured triangle -shaped, the contained angle is read out by the electron protractor, and the user inputs the back by the direct conversion department triangle -shaped another side of calculation module (the branch islong) with length value and/or angle value through the data input module to show the branch is long by the long display screen of branch.