We propose to implement simultaneous multi-mode-biased modal wavefront sensor (MMBWS) by utilizing a multiplexed computer-generated holographic element (MCGHE). The theoretical treatments of MCGHE used as MMBWS is presented. To realize the MCGHE, three multiplexed computer-generated holograms (MCGHs) are designed by coding 4, 10 and 20 Zernike aberration modes, respectively. Several critical problems relevant with the designing of MCGH are discussed. The performance of detecting single and multiple aberration modes by employing MCGH is numerically simulated. The results indicate that, within typical range of amplitude, the tested aberration modes can be responded by MMBWS if they are identical with those coded in the MCGH, and the sensitivities corresponding to each mode are different. Once the number of coded aberration modes is small, the sensitivity of the single mode will be large enough; the more the aberration modes are coded , the more severe erasure effect among the aberration modes will exist, thus the sensitivity of both the single and the multiple modes will be affected.