Due to the limitation of various conditions in the actual measurement, such as non-ideal 5050 beam splitter, balanced homodyne detector and interference efficiency, which are adverse to characterizing the squeezed state by the balanced homodyne detection (BHD) system. On the basis of the theoretical background of the BHD, the influence of the non-ideal BHD including the splitter ratio of 5050 beam splitter, the common mode rejection ratio (CMRR) of BHD and the interference efficiency on the measured squeezing degree are analyzed quantitatively, and the function of the deviation value is built with the real squeezing degree, splitter ratio of 5050 beam splitter, interference efficiency and CMRR. The result is very important for quantify the measuring error, and infer the real squeezing degree from the measured squeezing degree.