Evaluation of pilot's in-flight workload is a significant consideration for the safety of civil aviation. However, some errors may be brought in the measurement and the recording of objective parameters. Based on a multidimensional workload evaluation, the time delay of eye movement and its impacts on workload evaluation are analyzed. The results shows that within a certain limit of error around 300 ms, varying from pilots to pilots, workload can keep the main information of the original workload. As the error increases, the workload may become unreliable. As a consequence, the time-delay error of eye movement should be controlled within a limited scale to ensure the validity and reliability of workload.