There are many methods to match the shock spectrum in the laboratory，one of which is optimization method. This paper modifies. Rountree's Model. The shock spectrum forms which can be matched are more than Rountree's ordinary method. In order to assure the app1icabi1ity of this modification，a test is made on the 300kg electrodynamic shaker which is control1ed by a TRS-80 micro-computer， and the accuracy is satisfactory.