Abstract: In the linear induction accelerator, the power supply of rectifier loop is constant current sources. This article studied two kinds of voltage controlled constant current sources(VCCS) with operational amplifiers based on floating load and grounded load. From theory, simulation and experiment, their differences in configuration, operation character and output were comparatively studied. The results point out that the two kinds of VCCS can both produce the output in anticipation, and the floating-load VCCS can provide a more steady current output, fulfilling the future engineering requirements.