By optimizing the chromatographic conditions and sample pretreatment conditions, a method for determination of NMN content in NMN capsules and NMN tablets matrix was established based on high performance liquid chromatography, and the methodology was verified. The results showed that, the method with range of 5~500 μg/mL had a good linear relationship. The limit of detection (LOD, S/N=3) of NMN was 1.0 mg/kg, while the limit of quantitative (LOQ, S/N=10) was 3.0 mg/kg. The precision of the instrument was 0.3%. For NMN tablet samples, the stability of the method was 1.7% and the repeatability was 1.8%, while for NMN capsule samples, the stability of the method was 0.6%, and the repeatability RSD value was 0.6%. The recovery of NMN in NMN tablets and NMN capsules was between 90.9% and 108.9% with the RSD all no more than 1.9%. In conclusion, this method had good reproducibility, precision, stability and repeatability, could give accurate and reliable results, and could be used for the accurate determination of NMN in actual samples. Through the detection of 6 kinds of commercially available NMN products, NMN was detected in all samples, but the actual contents of some products were less than their nominal content. It was found that some products had the problem of false reporting of NMN content. This study would lay a methodological foundation for formulating the detection method standard of NMN content in NMN related dietary supplement products, and was of far-reaching significance for improving the quality of NMN related products and promote the convenient supervision of related industries.