Plane strain apparatus is an early-developed, relatively widely used, and yet immature experiment apparatus for soil testing. With the development of infrastructures, the plane strain tests and the related testing methods are applied to many project fields, showing their importance in engineering design and research. This paper reviews the historical development of plane strain apparatus at home and abroad, pointing out that it is necessary to explore a new kind of plane strain triaxial test apparatus for soil to achieve more reasonable and accurate plane strain data under complex stress loading conditions. For this purpose, by improving the structure of pressure chamber, loading system and control system, a new horizontal plane strain triaxial apparatus for soil has been developed. The results of the plane strain test are compared to those of the modified true triaxial test on remolded loess; and the strength parameters are determined using the new apparatus and compared with those of the conventional triaxial tests, showing the accuracy and reliability of the new horizontal plane strain triaxial apparatus. Finally, the failure characteristics determined by the new plane strain apparatus are compared to those obtained by the modified true triaxial apparatus, showing the applicability of the new plane strain apparatus in capturing the main features of soil localization.