Throuth computer simulation, we have numerically investigated the effect of pulse walkoff on optical pulse compression based on cross phase modulation in the normal dispersion regime of single mode fibers. It is found that even a small walkoff between the compressed bright pulse and the dark soliton can exert non ignorable influence on the bright pulse compression. Pulse walkoff not only leads to the degradation of the compression ratio and compressed peak power of the bright pulse,but also leads to a longer fiber length at which the width of the compressed bright pulse is minimum, and leads to the non-symmetry of the compressed bright pulse. An asynchronous coupling method is proposed to reduce the walkoff effect, and the results show that asynchronously coupling of the bright pulse with the dark soliton can efficiently improve the bright pulse compression relative to the synchronous coupling method.