To solve the shortcomings of non-intelligent, non-integrated and low efficiency of traditional method for measuring diameter at breast height (DBH), tree height and forest stand spatial structure parameters, a laser photogrammetric instrument for measuring forest based on the principle of photogrammetry, image processing technology, sensor technology and forest measurement was designed. The instrument was composed of CCD sensor, laser, LED flashlight, self-developed PDA and shell. There were three modular procedures which were compiled in the Java language and developed in Android Studio 2.2 systems development environment. The three modules were DBH measurement, tree height measurement and forest stand spatial structure parameters measurement. These three functions were achieved by obtaining parameters such as dip angle, azimuth and image information. The experiment of measuring DBH, tree height with 21 trees as samples and measuring forest stand spatial structure parameters with 15 reference trees in a plot as samples. Compared with the traditional measurement method, the mean absolute value of the relative error of DBH measurement was 2.55%, the tree height was 2.82%, the uniform angle index was 2.50%, the dominance was 2.86% and the measurement of the mingling was consistent with the traditional measurement method. The measurement accuracy of the instrument can meet the requirements of forestry survey. The method of using the laser photogrammetric instrument for measuring forest to measure the forest stand spatial structure parameters can be done which only required one person. Compared with the traditional measurement method, this method saved a half of labor and 31% of the working time. The instrument had a good prospect in the field of forestry basic investigation and forest stand spatial structure.