The invention discloses an easily-cut silicon brass alloy and a preparation method thereof. Chemical components of the silicon brass alloy include 59.2-63.5wt% of copper, 0.35-0.9wt% of silicon, 0.04-0.25wt% of lead and 0.22-0.38wt% of phosphor, other elements account for 0.005-1.1wt%, and the rest include zinc and inevitable impurities, wherein, the total amount of the copper, the zinc, the silicon, the lead and the phosphor is larger than 98.7wt%, and the other elements include at least one element selected from a group consisting of tin, nickel, iron, stibium and manganese. The preparation method is as follows: a method for alloying and for purifying and refining a covered and protected alterative scarfing cinder is adopted for smelting the easily-cut silicon brass alloy, then intermediate heat treatment is carried out at a temperature of 560-660 DEG C after coldworking with a working rate ranging from 4 percent to 25 percent, and a final finished product resulting from the working undergoes stress relief annealing at a low temperature of 380 DEG C. The invention has the advantage that the easily-cut silicon brass alloy has high tensile strength, excellent thermal formability, dezincing resistance, safe and sanitary performance and remarkable excellent cutting performance; meanwhile, the preparation process of the easily-cut silicon brass alloy is simple, the cost is low, and the easily-cut silicon brass alloy can be easily recycled.