Rapid and accurate determination of the nitrogen (N) and phosphorus (P) in the slurry/biogas slurry has been a technical bottleneck is urgently needed for the large-scale dairy farms in China on their ways of planting and breeding combination. Conventional wet chemical measuring methods in the laboratory were difficult to meet the practical demand of rapid quantitative determination on the N and P before recycling the dairy farm slurry back to the field. An indigenized rapid detection method of N and P through the full chain of slurry movement in large-scale dairy farms was developed based on the near-infrared (NIR), mid-infrared (MIR) and near-mid infrared (NIR-MIR) spectral fusion technology. A total of 144 slurry samples were collected along with the entire process links (manure collecting gutter, slurry tank, lagoon, etc.) from 27 large-scale dairy farms in Tianjin. The spectral data of 12 000~4 000 and 4 000~650 cm^-1 were collected by the Fourier transform near-infrared spectrometer (FT-NIRS) and mid-infrared spectrometer (FT-MIRS). Pretreatment methods involved the normalization, baseline and SNV were performed on the whole NIR, MIR and NIR-MIR data.NIR and MIR spectral characteristics were analyzed. The concentration gradient method was used for the sample diversity. NIR and MIR models of the total nitrogen (TN) and total phosphorus (TP) in the slurry were constructed by the partial least squares (PLS), interval partial least squares (IPLS) and synergy interval partial least squares (SIPLS). The results of slurry TN models were preferable, while the optimal models between the NIR and MIR were equivalent. The prediction performance of the TP model for the slurry was unsatisfactory that difficult of practical application. The $R^{2}_{pred}$ of the optimal SIPLS models for NIR and MIR were only 0.790 and 0.631, respectively. The residual predictive deviation (RPD) was 2.213 and 1.479 respectively. And the ratio of performance to interquartile range (RPIQ) was 3.616 and 2.351, respectively. In order to realize the simultaneous and effective determination and analysis of the N and P in the slurry meanwhile further improve the overall prediction performance of the model, the NIR-MIR fusion model of the N and P in the slurry was established integrated the NIR with MIR spectral data, with the spectral range of 12 000~650 cm^-1. The prediction performance behaved well overall. IPLS fusion model performed the optimum. The $R^{2}_{pred}$ was 0.970 and 0.861 respectively. RPD was 5.615 and 2.684 respectively. RPIQ was 12.874 and 4.394 respectively. It was better than the single NIR model and MIR model. In particular, the optimal fusion model of the TP was 0.071 and 0.170 which was higher than that of the single NIR and MIR models. The results showed that exact and rapid determination of the N and P through the full chain links of slurry movement in large-scale dairy farms via the near-mid infrared spectroscopy fusion technology could be available for the scientific slurry recycling to the farmland.