Abstract: PBL conditions over reclaimed grassland in northern China (49°19'N,119°55'E) are examined using the improved mesoscale model originally proposed by Nickerson et al.(1986).Basic results are presented as follows:ⅰ)the reclaimed section or the "heat island" has noon intencity of 4-6℃,the surface disturbante can be felt at 700 m AGL and conveciive perturbance at the PBL top,with the convective speed of 1-2cm/s; ii) once grassland is reclaimed on a large scale,the PBL climate will divelop into further aridity; iii) irrigation can alleviate the intensity and dryness of the "island" but fails to prevent the climate from aridization; iv) the local circulation in the PBL keeps its direction unchanged in 24 hrs,i.e.,wind blows toward the "island" at the height below 150-200 m at roughly of 2m/s and returns at higher levels with a slightly smaller speed.Further,moist flow can extend 30-50 km horizonally inside the reclamation.