Respiratory motion is one image degradation factor that affects the resolution and may cause artifacts in PET imaging. Respiratory gating technique is able to reduce the blurring effects but results in higher noise level. Conventional motion correction methods that model motion effects during or after image reconstruction not only increases reconstruction time, but also requires a gated or blurred attenuation map to reduce motion artifacts. This paper addresses the respiratory motion correction on sinogram data before reconstruction using a non-rigid motion model. It has the potential to reduce reconstruction time, and does not require gated attenuation maps.