The thickness and area of WS2 are critical for the optoelectronic response and bandgap. It is necessary to develop a large-area WS2 with an adjustable bandgap to obtain a high-performance optoelectronic device. In this work, large-area continuous WS(2-2x)Se2x (x = 0, 0.265, 0.39, 0.55) thin films were synthesized by the chemical vapor deposition. The bandgap range was adjusted by controlling the selenization time. Furthermore, the photodetectors Ag/WS(2-2x)Se2x/Ag with different Se compositions were explored. And a high-performance photodetector Ag/WS0.9Se1.1/Ag was constructed with a wide detection range of ultraviolet–visible–near infrared band. The responsivity, specific detection, and on/off ratio are 1.5 A/W,1.20 × 1011 Jones, and 2.9 × 105 at 365 nm, and the response time is 1.92 μs. This work provided a new synthetic method for growing bandgap-tunable transition metal disulfide and a new option for photoelectric detection in the ultraviolet–visible–near infrared region.