Two-dimensional (2D) WS2 offers great prospects for assembling next-generation optoelectronic and electronic devices due to its thickness-dependent optical and electronic properties. However, layer-number-controlled growth of WS2 is still a challenge up to now. This work presents controlled growth of bilayer WS2 triangular flakes by carbon-nanoparticle-assisted chemical vapor deposition (CVD) process. The growth mechanism is also proposed. In addition, the field effect transistors (FETs) based on monolayer and bilayer WS2 are also fabricated and investigated. The bilayer FET displays a mobility of 34 cm2·V-1·s-1, much higher than that of the monolayer FET. The high figures of merit make bilayer WS2 a promising candidate in high-performance electronics and optoelectronics.