This invention relates to a lock core structure that can be rapidly installed in locks and prevent parts thereof from being detached. The lock core structure mainly comprises a sleeve, a shaft, plural lower pins, plural upper pins, a cover and plural springs. The sleeve has a channel therethrough. The sleeve has plural chambers in a wall thereof extending normal to an axis of the sleeve. The shaft is received within the channel. The shaft has a keyway with an opening for receiving the key to be driven by the key to rotate an angle to unlock the lock. The shaft has plural through holes corresponding to the chambers. Each of the lower pins has a cap secured in the through holes and a body extended from the cap, projectable into the keyway. Each of the plural upper pins is slidably received in the chambers, and deposed against each of the lower pins respectively. The cover covers the chambers and is secured to the sleeve. Each of the plural springs is deposed in the chambers with one end against each the plural upper pins and with another end against the cover.