GB/T 8658-2025 is specifically aimed at emulsion coalescence styrene-butadiene rubber raw rubber, and stipulates the determination method of its combined styrene content - refractive index method. The standard specifies the test principle, required instruments, operation steps and result calculation method, which is suitable for mass detection of this type of rubber raw rubber. It can unify the detection method and ensure the accuracy of the data. It provides a reliable technical basis for rubber production quality control, product performance evaluation and application selection.