The invention discloses an ultrasonic contrast agent and a preparing method thereof and belongs to the field of ultrasonic imaging agents. The ultrasonic contrast agent is composed of a shell membrane material and an inert gas, wherein the shell membrane material comprises phospholipid and albumin, and the weight ratio of albumin to phospholipid is (1:4)-(3:4); the inert gas is sulfur hexafluoride or perfluoropropane. The particulate size of 80% of microbubbles of the microbubble ultrasonic contrast agent is smaller than 2 microns, particulate size distribution is uniform, dispersity is higher than that of SonoVue in the market, and in-vivo myocardial perfusion effect is better; the ultrasonic contrast agent is suitable for myocardial microcirculation reperfusion development, has a good development effect and low cost, is easy to store, and has broad clinical application prospects.