Over the past decades, observations of the cosmic microwave background (CMB) have established the standard cosmological model. In the future, 21cm signals from neutral hydrogen have great potential for cosmological and astrophysical studies. In this talk, I will review the previous CMB observations and how it established the ΛCDM cosmology model. Then I will discuss the instrumentation and calibration of the Cosmology Large Angular Scale Surveyor (CLASS) and the Simons Observatory (SO). At the end, I will discuss how we can use the 21cm observation as a powerful probe to study cosmology, and introduce our novel mapping method for 21cm interferometric data.