The invention discloses a preparation method of a WC cemented carbide with adjustable alignment of plate-shape grains. According to the theoretical composition of the cemented carbide, the weighed W powder is composed of two raw W materials with significantly different particle sizes in a certain mass ratio. Also graphite powder and Co powder are weighed. W—C—Co powder is subjected to planetary ball milling with controlled process parameters; then, after plasma-assisted ball milling, W—C—Co composite powder composed of small-sized lamellar W sheets and large-sized lamellar W sheet is obtained; Finally dense cemented carbide containing plate-shape WC grains is obtained by press molding of the ball milled power and in-situ carbonization through sintering at a high temperature. The invention not only provides simple preparation process with low energy consumption, but also can regulate the degree of orientated alignment of the plate-shape WC in the sintered block. Besides, the mechanical properties of the WC—Co cemented carbide containing plate-shape WC grains are optimized, so that the cemented carbide has excellent overall mechanical properties.