This paper considers robust CDMA receiver design and jamming evaluation under disguised jamming, where the jammer generates a fake signal using the same spreading code, constellation and pulse shaping filter as that of the authorized signal. First, we analyze the performance of conventional CDMA systems under disguised jamming, and show that due to the symmetricity between the authorized signal and the jamming interference, the receiver cannot really distinguish the authorized signal from jamming, leading to complete communication failure. Second, by exploiting the small time difference between the authorized signal and the jamming interference, the conventional CDMA receiver can be redesigned to achieve robust performance under disguised jamming. More specifically, we propose to estimate the authorized signal, the phase and power level or range of the jamming interference by minimizing the MSE between the received signal and the jammed signal, which is the sum of the authorized signal and the disguised jamming. The effectiveness of the proposed approach is demonstrated through simulation examples. It is shown that with the proposed receiver design, the BER performance of CDMA can be improved significantly under disguised jamming, and an analytical evaluation about jamming can also be obtained.