Volt-ampere characteristic(I-V) curve is one of the most important characteristics of solar arrays, and is an indispensable reference for field performance testing and designing of concentrating photovoltaic power generation system. However, customers can only get the curve under standard condition from manufacturers, but the actual operating environment varies widely. There are two difficulties to get a continuous and accurate I-V curve in any conditions, one is a variable resistor ranges from 0 to infinity; the other is wide range of measured objects which makes it inaccurate when measuring small signals. This paper uses capacitor charging method to simulate a variable resistor, and presents a method that combining a digital potentiometer and an instrumentation amplifier to get a flexible, programmable gain amplification circuit to solve the aforementioned difficulties. Besides, a touch screen with friendly user interface makes the tester easier to use, and the capability of data storage in SD card facilitates further analysis of the data.