In this paper, a new test method to determine biaxial flexural tensile strength of cement based materials is proposed. A mortar triangular plate specimen is supported on three small spherical silver balls and loaded externally on a small spherical silver ball from the center of gravity of specimen. Yield line theory (YLT), which is a kinematic method of plastic analysis, is used to drive a simple equation for biaxial flexural tensile strength of cement based materials. In order to verify the derived equation, lots of triangular and prism mortar specimens were produced and tested according to the proposed model and three-point flexural test, respectively. Moreover, finite element analysis is also used to verify the derived equation and the results obtained from the experimental studies. It was concluded that FE analysis and experimental studies verified the proposed method and the derived closed-form equation for biaxial tensile strength of cement based materials. Experimental results also exhibited that biaxial tensile strength measured by proposed method is about 22% lower than that of the flexural strength obtained from three-point flexural test.