The invention discloses a mechanism for preventing a card from overturning in a card case. The mechanism is characterized in that: the mechanism comprises a pressing card mechanism and at least a set of overturn prevention mechanism; two relative side plates of the card case (card storage case) are respectively provided with a vertical long strip guide groove used for elevating guiding of the pressing card mechanism; two sides of the pressing card mechanism are provided with a guiding shaft or a guiding sheet; one side plate of the card case is provided with a sidewall guide rail used for horizontal guiding of the overturn prevention mechanism, and quantity of the sidewall guide rail is equal to quantity of the overturn prevention mechanism; the overturn prevention mechanism comprises an installation support and a locking plate; a front end of the installation support is provided with a locking plate rotating shaft, and both the locking plate and a reset torsion spring are sleeved on the locking plate rotating shaft; one end of the reset torsion spring is provided on the installation support, and the other end of the reset torsion spring is provided on the locking plate. According to the invention, the card is effectively and automatically prevented from overturning, operation is convenient, and conception is ingenious.