A　specialized　experimental　device　was　utilized　to　investigate　the　influence　of　ultrasound　on　the　crystallization　characteristics　of　magnesium　ammonium　phosphate　(MAP);　the　crystallization　metastable　zone　width,　induction　period,　reaction　rate,　and　the　crystal　shape　of　MAP　were　analyzed　in　detail.　The　results　showed　that　the　critical　pH　value　of　the　supersaturated　MAP　solution　would　decrease　by　0.14,　0.21,　and　0.38　with　ultrasonication　of　4　mmol/L　MAP　reaction　solutions　at　150,　250,　and　350　W,　respectively.　Moreover,　the　metastable　zone　width　gradually　narrowed　with　increasing　ultrasonic　power,　and　the　induction　period　of　MAP　solutions　could　be　shortened　from　340　s　to　the　range　from　50　to　100　s　while　increasing　the　ultrasound　power　to　the　range　from　150　to　200　W.　However,　there　was　a　slight　change　in　the　induction　period　as　the　increase　in　ultrasonic　power　continued.　It　was　also　observed　that　the　crystallization　reaction　rate　of　MAP　could　be　accelerated　significantly　by　ultrasonication,　and　the　plateaus　of　the　MAP　crystallization　reaction　rate　curve　nearly　vanished　as　the　ultrasonic　power　increased.　Furthermore,　more　uniform,　more　complete,　and　fast　growth　of　the　produced　MAP　crystal　as　the　ultrasound　power　increased　was　observed　from　scanning　electron　microscopy　(SEM)　images.　©　2016,　Science　Press.　All　right　reserved.