Abstract: The configuration of high velocity arc spraying(HVAS) gun was optimized;the atomized particle velocity of the HVAS gun was measured by the Spraywatch-2i monitor system.A comparative study was carried out to investigate the microstructure and properties of the coatings produced by the original gun and the modified gun using 3mm diameter Al and 3Cr13 wires.The results indicated that angle and the distance from the nozzle to the meeting point of the two wires may have a strong influence on the characteristics of the in-flight droplets and the coatings,and the existing of wires and wire guides exited in the mater jets also affected the distribution of the air-flow field.Using the optimized gun,the atomized particle velocity is increased remarkably,and the coating microstructure and properties are improved relatively.The adhesion strength of the Al and 3Cr13 coatings deposited by the modified gun increased 55% and 39% respectively,and the hardness increased 26% and 9% respectively.The microstructure of the coatings was more dense and homogenous,and the porosity also decreased a little.When spraying 3Cr13,the highest particle velocity is about 210 m/s in the range of 170-270 mm from the nozzle to the meeting point of the two wires.