Abstract: The effects of modifiers polyvinyl butyral, polyacrylate and polystyrene on size stability, mechanical properties and thermal stability of moulding compound were investigated, and the dynamic mechanical properties and microstructure of fracture surface of modified systems were studied with dynamic mechanical analysis(DMA)and scanning electron microscope(SEM). The results showed that moulding plastic had the best dimension stability when polyvinyl butyral, polyacrylate and polystyrene were added 20%, 20% and 10%, respectively. The impact strength and bending strength of urea-formaldehyde resin molding plastic modified with 20% polyvinyl butyral were 2.55 kJ/m² and 88.3 MPa respectively, and increased by 49.1% and 63.2% comparing with unmodified compound. Polyacrylate could improve the low temperature resistance of molding compound, and moulding compound modified with polyvinyl butyral had good high-temperature performance; The DMA test results showed that polyvinyl butyral and polyacrylate had the toughening effects on the moulding compound, and the compatibility with urea-formaldehyde resin was better. The moulding compound modified with polystyrene could not be toughened. In addition, fracture surface of moulding compound modified with polyvinyl butyral and polyacrylate appeared gliding fracture and the compound modified with polystyrene appeared brittle fracture.