The invention relates to the technical field of medical equipment, and specifically discloses a disposable safe blood taking needle, and an assembling method and a use method of the disposable safe blood taking needle. When a needle core of the disposable safe blood taking needle is on an initial fixing position, a spring is in a stretched state and is used to store elastic potential energy. After a trigger portion is pressed to trigger the needle core, the needle core moves to an acupuncture limited position, so depth of a needle tip pierced skin is controllable, preventing the needle tip from piercing too deep. After blood is taken, the needle tip automatically enters a housing, preventing the needle tip from exposing and hurting people. The spring in the above structure provides potential energy used for ejection by stretching stored energy, and the spring is compressed to store energy under the action of the ejection potential energy, so as to provide retraction potential energy for the needle tip to automatically retract. Since the spring is sleeved on the needle core, the spring also has a guiding function in ejection and retraction. The spring has multiple functions. The needle is clever in design concept. The disposable safe blood taking needle is simple in structure and low in production cost, and the assembling method and the use method are relatively simple.