Implementations of this disclosure provide for certificate application operations. An example method includes sending, from a terminal device, a subscription topic name to a gateway to establish a data transmission channel between the terminal device and the gateway; receiving by the terminal device, via the data transmission channel, a certificate installation instruction from a certificate server; generating, by the terminal device, a user certificate request based on the certificate installation instruction; sending the user certificate request to the certificate server; and receiving, via the data transmission channel, a user certificate from the certificate server.