Abstract: In order to improve precision of rhomb-type achromatic A/4 phase retarders,based on the positive and negative delay error of A/4 phase retarders and larger refractive index,high precision retarders were designed.The retarder was analyzed and validated in experiments,and the data of high precision λ/4 phase retarder were obtained.It is shown at the retardation curve within the range of 350nm to 2000nm that retardation is 90°at two wavelengths and the maximal retardance error is smaller than 0.04°.Comparing with conventional retarders,the new retarder not only extends achromatic range,but also improves achromatic precision.The results are helpful to design high precision λ/4 phase retarders.