A video bit rate control method, for controlling the bit rate of video bit streams within a periodical time interval, comprising: according to a pre-set first bit rate value and a code size generated in a previous period of time, generating a first quantization parameter; according to a pre-set second bit rate value and the code size generated in the previous period of time, generating a second quantization parameter; comparing the first quantization parameter with the second quantization parameter; if the first quantization parameter is greater than or equal to the second quantization parameter, coding an image frame in a current period of time by using the first quantization parameter; and if the first quantization parameter is less than the second quantization parameter, coding the image frame in the current period of time by using the second quantization parameter; wherein the first bit rate value is a predetermined target average bit rate, which is a fixed value in each periodical time interval, the second bit rate value is the predetermined upper limit value of bit rate; characterized in that according to the pre-set first bit rate value and the code size generated in the previous period of time, generating the first quantization parameter comprises: dividing the periodical time interval into N time subintervals, wherein N is greater than 1; generating the first and second quantization parameters to make the first average bit rate satisfy the following formula: ∑ n = 1 N the first average bite rate of the nth time s u b int erval N = the first bite rate value; and performing bit rate adjustment to the first average bit rate of each time subinterval, so as to obtain a second average bit rate of each time subinterval, and make the second average bit rate satisfy the following formula: ∑ n = 1 N the sec ond average bite rate of the nth time s u b int erval N = the f irst bite rate value. according to a pre-set first bit rate value and a code size generated in a previous period of time, generating a first quantization parameter; according to a pre-set second bit rate value and the code size generated in the previous period of time, generating a second quantization parameter; comparing the first quantization parameter with the second quantization parameter; if the first quantization parameter is greater than or equal to the second quantization parameter, coding an image frame in a current period of time by using the first quantization parameter; and if the first quantization parameter is less than the second quantization parameter, coding the image frame in the current period of time by using the second quantization parameter; wherein the first bit rate value is a predetermined target average bit rate, which is a fixed value in each periodical time interval, the second bit rate value is the predetermined upper limit value of bit rate; characterized in that according to the pre-set first bit rate value and the code size generated in the previous period of time, generating the first quantization parameter comprises: dividing the periodical time interval into N time subintervals, wherein N is greater than 1; generating the first and second quantization parameters to make the first average bit rate satisfy the following formula: ∑ n = 1 N the first average bite rate of the nth time s u b int erval N = the first bite rate value; and performing bit rate adjustment to the first average bit rate of each time subinterval, so as to obtain a second average bit rate of each time subinterval, and make the second average bit rate satisfy the following formula: ∑ n = 1 N the sec ond average bite rate of the nth time s u b int erval N = the f irst bite rate value. dividing the periodical time interval into N time subintervals, wherein N is greater than 1; generating the first and second quantization parameters to make the first average bit rate satisfy the following formula: ∑ n = 1 N the first average bite rate of the nth time s u b int erval N = the first bite rate value; and performing bit rate adjustment to the first average bit rate of each time subinterval, so as to obtain a second average bit rate of each time subinterval, and make the second average bit rate satisfy the following formula: ∑ n = 1 N the sec ond average bite rate of the nth time s u b int erval N = the f irst bite rate value.