In non-homogeneous environment, traditional space-time adaptive processing doesn’t effectively suppress interference and detect target, because the secondary data don’t exactly reflect the statistical characteristic of the range cell under test. A novel methodology utilizing the direct data domain approach to space-time adaptive processing (STAP) in airborne radar non-homogeneous environments is presented. The deterministic least squares adaptive signal processing technique operates on a “snapshot-by-snapshot” basis to determine the adaptive weights for nulling interferences and estimating signal of interest (SOI). Furthermore, this approach eliminates the requirement for estimating the covariance through the data of neighboring range cell, which eliminates calculating the inverse of covariance, and can be implemented to operate in real-time. Simulation results illustrate the efficiency of interference suppression in non-homogeneous environment. In a non-homogeneous environment, traditional space-time adaptive processing does not effectively suppress interference and detect targets, because the secondary data do not exactly reflect the statistical characteristic of the range cell under test. A novel methodology utilizing the direct data domain approach to space-time adaptive processing (STAP) in airborne radar non-homogeneous environments is presented. The deterministic least squares adaptive signal processing technique operates on a “snapshot-by-snapshot” basis to determine the adaptive weights for nulling interferences and estimating signal of interest (SOI). This approach eliminates the requirement for estimating the covariance through the data of neighboring range cell, which eliminates calculating the inverse of covariance, and can be implemented to operate in real-time. suppression in non-homogeneous environment.