This paper applied ab initio theoretical studies on the complex of the π bond in C2H2 and nHX(n=1 8;X=F,Cl,Br,I),formed by typical X-H···π bond complexes in geometry and energy system is described and analysed,the results demonstrated that,C2H2···nHX(n=1 8;X=F,Cl,Br,I), with increasing halogen atomic number,from HF to HI,when hydrogen halide with the same number,the complex system of X-H···π bond length and other parameters showed a periodic increase;however,with the increase of the number of hydrogen halides,the binding energy of complex with n≤6,present in the overall increasing trend;and when n=6 reaches the maximum,in this case the π bond in C2H2 with hydrogen halide maximum capacity the limit has been reached, indicating that the π bond of C2H2···(HX)n up to six hydrogen halide molecules interactions to the formation of X-H···π bond complexes,that is to say X-H···π bond in C2H2···nHX complex have saturation property,and in the n=6 reach saturation state.