The paper presents the engineering background of capacitor tap in high frequency circuit, and discusses the actual effect of source and load on the LC tank, as well as the practical value of partial access method to solve the problem. Based on the elementary circuit theory and impedance transformation formula, equivalent calculation of capacitor tap is carried out respectively. The paper puts forward the error problem, and illustrates the reason by means of analysis. Finally, Software multisim is used to test the design circuit, and simulating results demonstrate the accuracy of the theory analysis and calculation.