A method for entity authentication in a resource-limited network, characterized in comprising: sharing a Pre-Shared key between an entity A and an entity B; sending, by the entity A, an authentication request message to the entity B, characterized in that the authentication request message comprises SN1 obtained in that the entity A generates a random number N1 and calculates SN1=N1 ⊕ PSK, wherein the symbol ' ⊕ ' represents a bitwise exclusive or operation; sending, by the entity B, an authentication response message to the entity A after receiving the authentication request message sent by the entity A, wherein sending, by the entity B, the authentication response message to the entity A specifically comprises: calculating, by the entity B, N1=SN1 ⊕ PSK, obtaining RN1 by reversing the bit sequence of N1 tailfirst, and calculating SRN1=RN1 ⊕ PSK; constructing, by the entity B, the authentication response message and sending the authentication response message to the entity A, wherein the authentication response message comprises SRN1; and determining, by the entity A, the validity of the entity B according to the received authentication response message, wherein determining, by the entity A, the validity of the entity B according to the received authentication response message specifically comprises: after receiving, by the entity A, the authentication response message sent by the entity B, firstly, calculating, by the entity A, RN1=SRN1 ⊕ PSK, obtaining N1' by reversing the bit sequence of RN1 tailfirst, and determining whether N1' is equal to N1 generated by the entity A, wherein if N1' is not equal to N1, the entity A discards the authentication response message; if N1' is equal to N1, the entity A determines that the entity B is valid, which means that the entity A performs a successful authentication on the entity B. sharing a Pre-Shared key between an entity A and an entity B; sending, by the entity A, an authentication request message to the entity B, characterized in that the authentication request message comprises SN1 obtained in that the entity A generates a random number N1 and calculates SN1=N1 ⊕ PSK, wherein the symbol ' ⊕ ' represents a bitwise exclusive or operation; sending, by the entity B, an authentication response message to the entity A after receiving the authentication request message sent by the entity A, wherein sending, by the entity B, the authentication response message to the entity A specifically comprises: calculating, by the entity B, N1=SN1 ⊕ PSK, obtaining RN1 by reversing the bit sequence of N1 tailfirst, and calculating SRN1=RN1 ⊕ PSK; constructing, by the entity B, the authentication response message and sending the authentication response message to the entity A, wherein the authentication response message comprises SRN1; and determining, by the entity A, the validity of the entity B according to the received authentication response message, wherein determining, by the entity A, the validity of the entity B according to the received authentication response message specifically comprises: after receiving, by the entity A, the authentication response message sent by the entity B, firstly, calculating, by the entity A, RN1=SRN1 ⊕ PSK, obtaining N1' by reversing the bit sequence of RN1 tailfirst, and determining whether N1' is equal to N1 generated by the entity A, wherein if N1' is not equal to N1, the entity A discards the authentication response message; if N1' is equal to N1, the entity A determines that the entity B is valid, which means that the entity A performs a successful authentication on the entity B.