The laser excitation fluorescence spectra of CaOH A-X(100)-(000) transitions were investigated. The assignments were made, and the molecular constants of A2II1/2(100) state were derived by least-squares fitting to be B =0.337097 (10), D = 0.877(5)×10-6, and P=-0.04039(2)cm-1. The rotational temperature of CaOH was also derived from the relative intensities of the rotational lines to be TR=308K.