This　paper　determines　elastic　constant　change　of　welding　heat　affect　zone　(HAZ)　of　TA15　titanium　alloy　by　electronic　beam　welding　(EBW)　using　ultrasonic　method.　The　ultrasonic　system　developed　can　measure　elastic　constants　of　the　materials　for　limited-size　zone　and　the　gradient　change　curve　of　the　HAZ　Young＇s　modules　is　determined.　Experimental　results　show　the　modulus　changes　obvious　from　the　base　material　to　welding　seam　and　electronic　beam　welding　leads　to　the　change　of　mechanical　properties　of　HAZ.　This　will　be　helpful　to　study　the　affect　of　electronic　beam　welding　to　the　HAZ　macro-mechanical　properties　and　improve　electronic　beam　welding　processing.