A resource allocation method includes the following steps: receiving a trigger frame signal, analyzing the trigger frame signal for acquiring at least one first user information field, determining at least one first random access resource unit number according to the at least one first user information field, decreasing a countdown parameter to generate a first countdown result according to the at least one first random access resource unit number, determining whether to continuously receive the trigger frame signal according to the first countdown result, and selecting a first random access resource unit from multiple random access resource units of the at least one first user information field when the trigger frame signal is not continuously received.