The 21 cm global spectrum provides an excellent window to observe the evolution of the early Universe. A high impedance receiver can be used in the global spectrum experiment, which offers a nearly uniform response over a large relative bandwidth, thus breaking the limitation imposed by the impedance matching between the antenna and receiver. This paper analyzes the measurement precision of the high-impedance receiver in the global spectrum experiment. We consider the main systematic errors: the vector network analyzer measurement error, the temperature measurement error, and the gain stability error. We use a Monte Carlo simulation to generate 10,000 sets of error combinations, and assess their impacts on observational results. For our experiment setup, we find that the level of systematic error is about 35 mK. This result is applicable to the Hongmeng Project (also known as the Discovering Sky at the Longest wavelength or DSL project), which will deploy an array of satellites on the cislunar orbit by a single rocket launch, to make low frequency imaging and global spectrum measurements. One of the satellites is dedicated to the 21 cm global spectrum observation in the 30–120 MHz frequency range, which employs a multi-receiver design scheme, to minimize systematic effects by cross-comparison of different receiving channels. The high-impedance channel is one to be used. Thus, within an acceptable range of systematic errors, the high-impedance receiver can provide a good measurement of the 21 cm signal, even if the 21 cm signal feature spans a broad frequency range.