The present invention provides a method and a device for acquiring point cloud data in the absence of GNSS signals, said method comprising: re-sampling line data obtained from a topographic map, so as to obtain discrete line data; simulating and generating a pulse per second (PPS); using a distance measuring instrument for counting and sampling the count, when a pulse per second (PPS) is detected, calculating the sum of the counts per second measured by the distance measuring instrument, and according to the distance measuring instrument parameter, position information of the previous moment, and the line data, calculating position information of the current moment; according to the position information of the current moment, simulating a GNSS satellite protocol; using a point cloud data acquisition module to parse the GNSS satellite protocol to perform time synchronization, and controlling a lidar to acquire point cloud data; using an inertial measurement module to parse the GNSS satellite protocol and recording orientation and position data in real time, so as to generate POS data containing position and orientation information; and using the distance measuring instrument data and external control points to optimize the POS data, so as to obtain precise point cloud data. Compared with the existing acquisition methods and devices, the present invention has high efficiency and high precision.