We carried out photometric observations of the SX Phe star BL Cam in 2014 , 2017 and 2018 using Nanshan 1-m telescope .
In addition to the dominated frequency of 25.5790 ( 3 ) cd ^ { -1 } and its two harmonics , an independent frequency of 25.247 ( 2 ) cd ^ { -1 } , which is a nonradial mode frequency , was detected from the data in 2014 .
A total of 123 new times of light maxima were determined from our light curves in the three years , which , together with that published in the literature , were used to analyze the O - C diagram .
The change rate of the main period was derived as ( 1/P ) ( dP/dt ) = -2.39 ( 8 ) \times 10 ^ { -8 } yr ^ { -1 } , which is lower than that published in previous literature .
A periodical change with a period of 14.01 ( 9 ) yr was found in the residuals of the O - C curve fitting .
If it was caused by the light-time effect , BL Cam should be a binary system .
The mass of the companion was restricted as low as that of a brown dwarf .
No evidence of the triple system suggested by previous authors was shown in our analysis .