A mobile solar simulator is a requisite apparatus for conducting the field test prior to launching a coded solar-sensor-equipped satellite, which can provide simulated sunlight signal and sunlight vector signal for the test. This study provides a discussion on the structural configuration and working principle of the mobile solar simulator. Specifically, we present the description and design of the LED array light source and the collimating optical system in the device. For the light source, a power formula is applied to determining the number of LEDs, and the Sparrow criterion is considered to be the basis for analyzing the LED spacing. In particular, the array spacing is determined from the effect of irradiation uniformity. Furthermore, a mathematical model of cylindrical mirror is established based on the principle of an edge ray. The design and simulation of the collimating optical system are performed using the LightTools software. The experimental results denote that the mobile solar simulator has an irradiation area of 10 mm×50 mm, where the irradiance becomes 393 W·m -2 at a working distance of 50 mm. Further, the irradiation nonuniformities at three incident angles of -13°, 0°, 38° are better than ±7.3%, and the exit angle is 0.78°. This solar simulator can complete the encoded solar sensor field test after the installation of a satellite.