A new method is proposed to determinate the parameters of the gratings at the same time by means of the diffractive efficiencies ratio (+1/－1) and simulated annealing algorithm. We make use of the diffraction orders efficiency ratio (m=+1,－1) decrease the error result from the varied degree surface roughness,the aberration in the structure period and the medium distributing uneven etc,in order to ensure to calculation precision in the optimized method. In the experiment of determining the Volume Phase Holographic Grating's parameters,the error of the result is not over l%,so it demonstrates the metrology's validity and feasibility. At the same time,It has a lot of advantages such as no damage,simplicity of measurement,facility of manipulation,good stability and so on.. we believe that the metrology will become the powerful instrument in measurement the grating constant.