In order to solve the problems on low-cost water treatment, the utility model proposed hereby relies on adding and using oyster shell powder as a filter core material for the structure of the portable water purifier. Besides offering the primary functions of an effective water purifying outdoor portable device, the utility model offers the advantages of by-product recycling, utilization of a biodegradable filter core, as well as prevention of secondary environmental pollution. The proposed utility model belongs to a new generation of technologies for environmental protection and water treatment. Its low-cost highly efficient and easily-biodegradable filter material, oyster shell powder, makes it an environment-friendly water purifier for outdoor use which is convenient to carry.