The plasma sheath will be formed during aircrafts' reentry, and the formation of plasma sheath will seriously affect the spread of the waves, causing the communication barriers. In order to know the transmission characteristics of electromagnetic wave in plasma sheath, this paper deduces the precondition that electromagnetic wave can transmit and the computing method that electromagnetic waves transmit along different directions through theoretical analysis. At the same time, the characteristics of absorption of electromagnetic wave in plasma and reflection characteristics have been studied using the results derived from the theory, and the result has the very high accuracy.