Since the exciting discovery of graphene, there has been a huge growth in research in material science on finding novel nanostructured materials with advanced material properties. Recently, a novel two-dimensional material, i.e., phosphorene sheets with a characteristic puckered structure, has been explored. The study aims at providing a systematic investigation of the effect of atomistic defect on thermal-mechanical properties, such as Young's modulus, shear modulus, specific heat capacity, and linear coefficient of thermal expansion (CTE), of phosphorene sheets using molecular dynamics simulation incorporated with Nos,-Hoover Langevin thermostat. The calculation results show that the Young's modulus, shear modulus, specific heat capacity, and CTE of armchair and zigzag types of phosphorene sheets decrease with the increasing vacancy defect ratio. The specific heat capacity and linear CTE would rise with increasing temperature at low temperatures and converge to a constant value as temperature is larger than 600 K. Besides, the calculated specific heat capacity of the two types of phosphorene sheets all closely follows the Debye T (3)-law at low temperatures.