A multi-stream image processing method, comprising: generating a plurality of image streams (MS, SS1, SS2) by a former stage circuit according to a same image source, wherein the image streams comprises a main image stream and at least one sub image stream, and the resolution of the main image stream is higher than the resolution of the sub image stream; within a N-th image frame processing time period, storing a N-th sub image frame of the sub image stream by the former stage circuit in at least one current sub image storage block of a memory module and storing a N-th main image frame of the main image stream by the former stage circuit in a main image storage block of the memory module, wherein N is a positive integer equal to or larger than 2; within a first sub period of the N-th image frame processing time period, reading a N-1-th sub image frame of the sub image stream stored in a previous sub image storage block of the memory module by a latter stage circuit and processing the N-1-th sub image frame by the latter stage circuit; within a second sub period of the N-th image frame processing time period behind the first sub period, reading the N-th main image frame stored in the main image storage block by the latter stage circuit and processing the N-th main image frame by the latter stage circuit; retrieving frame processing information of the former stage circuit and the latter stage circuit, wherein the frame processing information comprises a former stage frame number and a storing row number of the image frame that the former stage circuit currently stores, and comprises a latter stage frame number and a reading row number of the image frame that the latter stage circuit currently reads; determining whether the former stage frame number and the latter stage frame number are the same; and when the former stage frame number and the latter stage frame number are the same, activating a synchronization mechanism of a synchronization circuit, wherein the synchronization mechanism is performed based on the storing row number and the reading row number. generating a plurality of image streams (MS, SS1, SS2) by a former stage circuit according to a same image source, wherein the image streams comprises a main image stream and at least one sub image stream, and the resolution of the main image stream is higher than the resolution of the sub image stream; within a N-th image frame processing time period, storing a N-th sub image frame of the sub image stream by the former stage circuit in at least one current sub image storage block of a memory module and storing a N-th main image frame of the main image stream by the former stage circuit in a main image storage block of the memory module, wherein N is a positive integer equal to or larger than 2; within a first sub period of the N-th image frame processing time period, reading a N-1-th sub image frame of the sub image stream stored in a previous sub image storage block of the memory module by a latter stage circuit and processing the N-1-th sub image frame by the latter stage circuit; within a second sub period of the N-th image frame processing time period behind the first sub period, reading the N-th main image frame stored in the main image storage block by the latter stage circuit and processing the N-th main image frame by the latter stage circuit; retrieving frame processing information of the former stage circuit and the latter stage circuit, wherein the frame processing information comprises a former stage frame number and a storing row number of the image frame that the former stage circuit currently stores, and comprises a latter stage frame number and a reading row number of the image frame that the latter stage circuit currently reads; determining whether the former stage frame number and the latter stage frame number are the same; and when the former stage frame number and the latter stage frame number are the same, activating a synchronization mechanism of a synchronization circuit, wherein the synchronization mechanism is performed based on the storing row number and the reading row number.