In this paper, we propose a linear dependent rate-quantization model for video enhancement layers encoding in H.264/AVC based scalable video coding (SVC). It is noted that the proposed model is applicable for different scalable structures, such as temporal, quality, spatial and combined scalability. Leveraging the base layer information (such as bitrate and quantization parameter), proposed model can accurately predict the number of bit required for the enhancement layer encoding. Such linear model demonstrates the high accuracy for bitrate estimation at enhancement layers, with the average prediction accuracy over 94%. It has the noticeable improvement from the existing works, without requiring additional complexity increase. Meanwhile, proposed model is applied to do the rate control for enhancement layers encoding. Experimental results show that the average bitrate mismatch error can be significantly reduced compared with the existing algorithms.