Spoofing will seriously threaten the application of global navigation satellite system (GNSS) like autonomous vehicle. A research spoofing generator will contribute to assess the threat of spoofing attack and help the anti-spoofing research. But the recent commercial of the shelf (COTS) spoofing generator are expensive and the technology implementation is sophisticated and complicated. To address the above problem and promote the GNSS safety-critical applications, a spoofing generator using vector tracking-based software-defined receiver is proposed in this paper. The spoofing generator aims to modify the raw signals by cancelling the actual signal. The connections between the spreading code and carrier and the states of the victim/spoofed receiver are established through vector-tracking. The actual signal can be predicted effectively and the spoofing signal will be generated at the same time. The experiment test results show that the spoofing attack signal can mislead the victim receiver to the designed trajectory effectively. Neither the tracking channels nor the positioning observations has abnormal changes during this processing period. The recent anti-spoofing methods cannot detect this internal spoofing easily. The proposed spoofing generator can cover all open-sky satellites with a good quality of concealment. With the superiority of programmability and diversity, it is believed that the proposed spoofing generator method based on an open source software-defined receiver with vector tracking architecture has a great value for GNSS anti-spoofing researches.