In the present paper, a new approach to rapid determination of compound fertilizer composition was introduced, namely first preparing aqueous solution of solid fertilizer, then predicting the compound fertilizer composition using the near infrared transmission spectra of the solution. Using the new method, models were built by means of PLS regression, and the standard errors of prediction of total nitrogen content, P2O5 content, and K2O content are 0.5, 0.7, 0.8, and 2.0, respectively. This has solved the problem of large prediction error for K content of compound fertilizer using near infrared reflectance spectroscopy due to the fact that KCl dose not have near infrared absorption, and achieved rapid analysis of all compositions of compound fertilizer in 5 minutes.