This paper presents a new method of measuring fat content in coconut milk at room temperature (25°C) based on the designed Y-type optical fiber measurement system and makes the analysis and evaluation of this system. The system consists of light source, Y-type optical fiber, signal amplification module, signal conversion module and microprocessor module. The new method of assessing the accuracy of the measurement system – R&R (Repeatability and Reproducibility) assessment method is introduced here. It makes the effective analysis and evaluation and judges the reliability of the Y-type optical fiber system, laying the foundation for obtaining high quality data. The results show that the designed measurement system has high precision and can satisfy the measurement of this kind of samples.