Hydroxyethyl Cellulose can be used as a thickener and cementing agent of workover fluid for oil wells. It helps to provide with the clear solution with a low fixed content, thus greatly reducing the damage to the structure of oil wells. The liquid with Hydroxyethyl Cellulose used for thickening gets easily decomposed by the acid, enzyme or oxidizing agent, and greatly enhances the ability of hydrocarbon recovery. In the oil well fluid, hydroxyethyl cellulose is used as the carrier of proppant. These fluids can be easily decomposed by the the processes described above.