We explored a two-dimensional (2D) binary compound consisting of arsenic and phosphorus by means of density functional theory (DFT) calculations. The geometry, electronic structure, and optical properties of monolayer, few-layer and bulk As1-xPx compounds with different composition ratio were investigated. We can achieve a more continuous tuning in band gap by change the composition and thickness. The band gap of As1-xPx monolayer was almost the same as that of phosphorene monolayer, regardless of the As concentration. However, the band gaps of few-layer systems decrease significantly. In the case of few layer systems, they can possess various band gap values those the pristine phosphorus system cannot reach. The direct-indirect band gap transition occurred at a certain threshold when the As concentration continuously increased. The more concentration of As was, the faster band gap decreased. The band gaps of their bulk systems were in the range of 03-0.4 eV, which is very close to that of bulk phosphorus and this was not sensitive to the composition and topological arrangement. The dielectric function calculations revealed that the optical properties of the arsenic phosphide systems were highly tunable by changing the composition and thickness. Overall, we propose that the tunable electronic and optical properties of the As1-xPx binary compounds make them great candidates for application in the field of electronics and optoelectronics. (C) 2016 Elsevier B.V. All rights reserved.